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ENGINEERING MATHEMATICS-ISECTION-B
DIFFERENTIAL CALCULUS
Successive Differentiation
Leibnitz Theorem and Applications
Taylors and MaclaurinsSeries Curvature
Asymptotes
Curve tracing
Functions of Two or More
Variables
Partial Derivatives of First and
Higher Order
Eulerrsquos Theorem on
Homogeneous Functions
Differentiation of Composite
and Implicit Functions
Jacobians
Taylorrsquos Theorem For A Function of Two Variables
Maxima and Minima of Functions of Two Variables
Lagranges Method of
Undetermined
Multipliers
Differentiation Under
Integral Sign
E-LEARNINGTopic Taylorrsquos seriesE-learning httpnptelacincourses12210401711
Topic Maclaurinrsquos seriesE-learning httpnptelacincourses12210401711
Topic Partial derivatives of first order amp its higher orderE-learning httpnptelacincourses12210100331
Topic Eulerrsquos theorem on homogeneous functions E-learning wwwnptelacincourses122101003downloadsLecture-31pdf
Topic Total differentialDerivatives of composite and implicit functionE-learning httpnptelacincourses12210100332
httpnptelacincourses12210100333
Topic Maxima and minima of function of two variablesE-learning httpnptelacincourses12210401710httpnptelacincourses12210100337httpnptelacincourses12210401726
Topic Lagrangersquos method of undermined multipliersE learning httpnptel ac incourses12210401727
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
119889119889119889119889119889119889119889119889
11988911988921198891198891198891198891198891198892
11988911988931198891198891198891198891198891198893 hellip hellip hellip hellip hellip hellip hellip
119889119889119899119899119889119889119889119889119889119889119899119899
119889119889111988911988921198891198893 hellip hellip hellip hellip hellip hellip hellip hellip hellip 119889119889119899119899
119889119889prime 119889119889primeprime119889119889primeprimeprime hellip hellip hellip hellip hellip hellip hellip hellip hellip119889119889119899119899
Example 1 Find the fourth derivative of tan x at 119889119889 = 1205871205874
Example 2 119894119894119894119894 119889119889 = 119860119860119890119890119898119898119889119889 + 119861119861119890119890119899119899119889119889 119875119875119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889
1198891198891198891198892 minus (119898119898 + 119899119899) 119889119889119889119889119889119889119889119889
+119898119898119899119899119889119889 = 0
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
Example 1 Find the fourth derivative of tan x at
Example 2
SOME STANDARD RESULTS1 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119889119889119898119898 = 119898119898
(119898119898minus119899119899)119889119889119898119898minus119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
2 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 (119886119886119889119889 + 119887119887)119898119898 = 119898119898(119898119898 minus 1)(119898119898 minus 2) hellip hellip hellip hellip hellip hellip (119898119898 minus 119899119899 +1)(119886119886119889119889 + 119887119887)119898119898minus119899119899 119886119886119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
3 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 1119886119886119889119889+119887119887
= (minus1)119899119899 119899119899 119886119886119899119899
(119886119886119889119889minus119887119887)119899119899+1
4 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894119900119900119875119875119900119900(119886119886119889119889 + 119887119887) = (minus1)119899119899minus1(119899119899minus1)119886119886119899119899
(119886119886119889119889+119887119887)119899119899
5 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119886119886119898119898119889119889 = 119898119898119899119899119886119886119898119898119889119889 (log119886119886)119899119899 6 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119890119890119898119898119889119889 = 119898119898119899119899119890119890119898119898119889119889
7 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 sin(119886119886119889119889 + 119887119887) = 119886119886119899119899sin119886119886119889119889 + 119887119887 + 119899119899 1205871205872
8 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 cos(119886119886119889119889 + 119887119887) = 119886119886119899119899cos119886119886119889119889 + 119887119887 + 119899119899 1205871205872
9 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax sin(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 sin119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
10 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax cos(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 cos119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
1
2
3
4
5
6
7
8
9
10
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
DIFFERENTIAL CALCULUS
Successive Differentiation
Leibnitz Theorem and Applications
Taylors and MaclaurinsSeries Curvature
Asymptotes
Curve tracing
Functions of Two or More
Variables
Partial Derivatives of First and
Higher Order
Eulerrsquos Theorem on
Homogeneous Functions
Differentiation of Composite
and Implicit Functions
Jacobians
Taylorrsquos Theorem For A Function of Two Variables
Maxima and Minima of Functions of Two Variables
Lagranges Method of
Undetermined
Multipliers
Differentiation Under
Integral Sign
E-LEARNINGTopic Taylorrsquos seriesE-learning httpnptelacincourses12210401711
Topic Maclaurinrsquos seriesE-learning httpnptelacincourses12210401711
Topic Partial derivatives of first order amp its higher orderE-learning httpnptelacincourses12210100331
Topic Eulerrsquos theorem on homogeneous functions E-learning wwwnptelacincourses122101003downloadsLecture-31pdf
Topic Total differentialDerivatives of composite and implicit functionE-learning httpnptelacincourses12210100332
httpnptelacincourses12210100333
Topic Maxima and minima of function of two variablesE-learning httpnptelacincourses12210401710httpnptelacincourses12210100337httpnptelacincourses12210401726
Topic Lagrangersquos method of undermined multipliersE learning httpnptel ac incourses12210401727
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
119889119889119889119889119889119889119889119889
11988911988921198891198891198891198891198891198892
11988911988931198891198891198891198891198891198893 hellip hellip hellip hellip hellip hellip hellip
119889119889119899119899119889119889119889119889119889119889119899119899
119889119889111988911988921198891198893 hellip hellip hellip hellip hellip hellip hellip hellip hellip 119889119889119899119899
119889119889prime 119889119889primeprime119889119889primeprimeprime hellip hellip hellip hellip hellip hellip hellip hellip hellip119889119889119899119899
Example 1 Find the fourth derivative of tan x at 119889119889 = 1205871205874
Example 2 119894119894119894119894 119889119889 = 119860119860119890119890119898119898119889119889 + 119861119861119890119890119899119899119889119889 119875119875119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889
1198891198891198891198892 minus (119898119898 + 119899119899) 119889119889119889119889119889119889119889119889
+119898119898119899119899119889119889 = 0
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
Example 1 Find the fourth derivative of tan x at
Example 2
SOME STANDARD RESULTS1 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119889119889119898119898 = 119898119898
(119898119898minus119899119899)119889119889119898119898minus119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
2 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 (119886119886119889119889 + 119887119887)119898119898 = 119898119898(119898119898 minus 1)(119898119898 minus 2) hellip hellip hellip hellip hellip hellip (119898119898 minus 119899119899 +1)(119886119886119889119889 + 119887119887)119898119898minus119899119899 119886119886119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
3 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 1119886119886119889119889+119887119887
= (minus1)119899119899 119899119899 119886119886119899119899
(119886119886119889119889minus119887119887)119899119899+1
4 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894119900119900119875119875119900119900(119886119886119889119889 + 119887119887) = (minus1)119899119899minus1(119899119899minus1)119886119886119899119899
(119886119886119889119889+119887119887)119899119899
5 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119886119886119898119898119889119889 = 119898119898119899119899119886119886119898119898119889119889 (log119886119886)119899119899 6 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119890119890119898119898119889119889 = 119898119898119899119899119890119890119898119898119889119889
7 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 sin(119886119886119889119889 + 119887119887) = 119886119886119899119899sin119886119886119889119889 + 119887119887 + 119899119899 1205871205872
8 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 cos(119886119886119889119889 + 119887119887) = 119886119886119899119899cos119886119886119889119889 + 119887119887 + 119899119899 1205871205872
9 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax sin(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 sin119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
10 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax cos(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 cos119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
1
2
3
4
5
6
7
8
9
10
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Differentiation of Composite
and Implicit Functions
Jacobians
Taylorrsquos Theorem For A Function of Two Variables
Maxima and Minima of Functions of Two Variables
Lagranges Method of
Undetermined
Multipliers
Differentiation Under
Integral Sign
E-LEARNINGTopic Taylorrsquos seriesE-learning httpnptelacincourses12210401711
Topic Maclaurinrsquos seriesE-learning httpnptelacincourses12210401711
Topic Partial derivatives of first order amp its higher orderE-learning httpnptelacincourses12210100331
Topic Eulerrsquos theorem on homogeneous functions E-learning wwwnptelacincourses122101003downloadsLecture-31pdf
Topic Total differentialDerivatives of composite and implicit functionE-learning httpnptelacincourses12210100332
httpnptelacincourses12210100333
Topic Maxima and minima of function of two variablesE-learning httpnptelacincourses12210401710httpnptelacincourses12210100337httpnptelacincourses12210401726
Topic Lagrangersquos method of undermined multipliersE learning httpnptel ac incourses12210401727
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
119889119889119889119889119889119889119889119889
11988911988921198891198891198891198891198891198892
11988911988931198891198891198891198891198891198893 hellip hellip hellip hellip hellip hellip hellip
119889119889119899119899119889119889119889119889119889119889119899119899
119889119889111988911988921198891198893 hellip hellip hellip hellip hellip hellip hellip hellip hellip 119889119889119899119899
119889119889prime 119889119889primeprime119889119889primeprimeprime hellip hellip hellip hellip hellip hellip hellip hellip hellip119889119889119899119899
Example 1 Find the fourth derivative of tan x at 119889119889 = 1205871205874
Example 2 119894119894119894119894 119889119889 = 119860119860119890119890119898119898119889119889 + 119861119861119890119890119899119899119889119889 119875119875119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889
1198891198891198891198892 minus (119898119898 + 119899119899) 119889119889119889119889119889119889119889119889
+119898119898119899119899119889119889 = 0
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
Example 1 Find the fourth derivative of tan x at
Example 2
SOME STANDARD RESULTS1 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119889119889119898119898 = 119898119898
(119898119898minus119899119899)119889119889119898119898minus119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
2 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 (119886119886119889119889 + 119887119887)119898119898 = 119898119898(119898119898 minus 1)(119898119898 minus 2) hellip hellip hellip hellip hellip hellip (119898119898 minus 119899119899 +1)(119886119886119889119889 + 119887119887)119898119898minus119899119899 119886119886119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
3 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 1119886119886119889119889+119887119887
= (minus1)119899119899 119899119899 119886119886119899119899
(119886119886119889119889minus119887119887)119899119899+1
4 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894119900119900119875119875119900119900(119886119886119889119889 + 119887119887) = (minus1)119899119899minus1(119899119899minus1)119886119886119899119899
(119886119886119889119889+119887119887)119899119899
5 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119886119886119898119898119889119889 = 119898119898119899119899119886119886119898119898119889119889 (log119886119886)119899119899 6 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119890119890119898119898119889119889 = 119898119898119899119899119890119890119898119898119889119889
7 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 sin(119886119886119889119889 + 119887119887) = 119886119886119899119899sin119886119886119889119889 + 119887119887 + 119899119899 1205871205872
8 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 cos(119886119886119889119889 + 119887119887) = 119886119886119899119899cos119886119886119889119889 + 119887119887 + 119899119899 1205871205872
9 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax sin(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 sin119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
10 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax cos(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 cos119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
1
2
3
4
5
6
7
8
9
10
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
E-LEARNINGTopic Taylorrsquos seriesE-learning httpnptelacincourses12210401711
Topic Maclaurinrsquos seriesE-learning httpnptelacincourses12210401711
Topic Partial derivatives of first order amp its higher orderE-learning httpnptelacincourses12210100331
Topic Eulerrsquos theorem on homogeneous functions E-learning wwwnptelacincourses122101003downloadsLecture-31pdf
Topic Total differentialDerivatives of composite and implicit functionE-learning httpnptelacincourses12210100332
httpnptelacincourses12210100333
Topic Maxima and minima of function of two variablesE-learning httpnptelacincourses12210401710httpnptelacincourses12210100337httpnptelacincourses12210401726
Topic Lagrangersquos method of undermined multipliersE learning httpnptel ac incourses12210401727
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
119889119889119889119889119889119889119889119889
11988911988921198891198891198891198891198891198892
11988911988931198891198891198891198891198891198893 hellip hellip hellip hellip hellip hellip hellip
119889119889119899119899119889119889119889119889119889119889119899119899
119889119889111988911988921198891198893 hellip hellip hellip hellip hellip hellip hellip hellip hellip 119889119889119899119899
119889119889prime 119889119889primeprime119889119889primeprimeprime hellip hellip hellip hellip hellip hellip hellip hellip hellip119889119889119899119899
Example 1 Find the fourth derivative of tan x at 119889119889 = 1205871205874
Example 2 119894119894119894119894 119889119889 = 119860119860119890119890119898119898119889119889 + 119861119861119890119890119899119899119889119889 119875119875119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889
1198891198891198891198892 minus (119898119898 + 119899119899) 119889119889119889119889119889119889119889119889
+119898119898119899119899119889119889 = 0
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
Example 1 Find the fourth derivative of tan x at
Example 2
SOME STANDARD RESULTS1 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119889119889119898119898 = 119898119898
(119898119898minus119899119899)119889119889119898119898minus119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
2 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 (119886119886119889119889 + 119887119887)119898119898 = 119898119898(119898119898 minus 1)(119898119898 minus 2) hellip hellip hellip hellip hellip hellip (119898119898 minus 119899119899 +1)(119886119886119889119889 + 119887119887)119898119898minus119899119899 119886119886119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
3 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 1119886119886119889119889+119887119887
= (minus1)119899119899 119899119899 119886119886119899119899
(119886119886119889119889minus119887119887)119899119899+1
4 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894119900119900119875119875119900119900(119886119886119889119889 + 119887119887) = (minus1)119899119899minus1(119899119899minus1)119886119886119899119899
(119886119886119889119889+119887119887)119899119899
5 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119886119886119898119898119889119889 = 119898119898119899119899119886119886119898119898119889119889 (log119886119886)119899119899 6 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119890119890119898119898119889119889 = 119898119898119899119899119890119890119898119898119889119889
7 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 sin(119886119886119889119889 + 119887119887) = 119886119886119899119899sin119886119886119889119889 + 119887119887 + 119899119899 1205871205872
8 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 cos(119886119886119889119889 + 119887119887) = 119886119886119899119899cos119886119886119889119889 + 119887119887 + 119899119899 1205871205872
9 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax sin(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 sin119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
10 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax cos(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 cos119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
1
2
3
4
5
6
7
8
9
10
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
119889119889119889119889119889119889119889119889
11988911988921198891198891198891198891198891198892
11988911988931198891198891198891198891198891198893 hellip hellip hellip hellip hellip hellip hellip
119889119889119899119899119889119889119889119889119889119889119899119899
119889119889111988911988921198891198893 hellip hellip hellip hellip hellip hellip hellip hellip hellip 119889119889119899119899
119889119889prime 119889119889primeprime119889119889primeprimeprime hellip hellip hellip hellip hellip hellip hellip hellip hellip119889119889119899119899
Example 1 Find the fourth derivative of tan x at 119889119889 = 1205871205874
Example 2 119894119894119894119894 119889119889 = 119860119860119890119890119898119898119889119889 + 119861119861119890119890119899119899119889119889 119875119875119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889
1198891198891198891198892 minus (119898119898 + 119899119899) 119889119889119889119889119889119889119889119889
+119898119898119899119899119889119889 = 0
The Process of Differentiating a function again and again is called successive Differentiation
If y be a function of x then its successive derivatives are denoted by
Example 1 Find the fourth derivative of tan x at
Example 2
SOME STANDARD RESULTS1 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119889119889119898119898 = 119898119898
(119898119898minus119899119899)119889119889119898119898minus119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
2 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 (119886119886119889119889 + 119887119887)119898119898 = 119898119898(119898119898 minus 1)(119898119898 minus 2) hellip hellip hellip hellip hellip hellip (119898119898 minus 119899119899 +1)(119886119886119889119889 + 119887119887)119898119898minus119899119899 119886119886119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
3 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 1119886119886119889119889+119887119887
= (minus1)119899119899 119899119899 119886119886119899119899
(119886119886119889119889minus119887119887)119899119899+1
4 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894119900119900119875119875119900119900(119886119886119889119889 + 119887119887) = (minus1)119899119899minus1(119899119899minus1)119886119886119899119899
(119886119886119889119889+119887119887)119899119899
5 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119886119886119898119898119889119889 = 119898119898119899119899119886119886119898119898119889119889 (log119886119886)119899119899 6 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119890119890119898119898119889119889 = 119898119898119899119899119890119890119898119898119889119889
7 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 sin(119886119886119889119889 + 119887119887) = 119886119886119899119899sin119886119886119889119889 + 119887119887 + 119899119899 1205871205872
8 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 cos(119886119886119889119889 + 119887119887) = 119886119886119899119899cos119886119886119889119889 + 119887119887 + 119899119899 1205871205872
9 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax sin(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 sin119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
10 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax cos(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 cos119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
1
2
3
4
5
6
7
8
9
10
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
SOME STANDARD RESULTS1 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119889119889119898119898 = 119898119898
(119898119898minus119899119899)119889119889119898119898minus119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
2 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 (119886119886119889119889 + 119887119887)119898119898 = 119898119898(119898119898 minus 1)(119898119898 minus 2) hellip hellip hellip hellip hellip hellip (119898119898 minus 119899119899 +1)(119886119886119889119889 + 119887119887)119898119898minus119899119899 119886119886119899119899 119894119894119894119894 119898119898119898119898119898119898119898119898 gt 119899119899
3 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 1119886119886119889119889+119887119887
= (minus1)119899119899 119899119899 119886119886119899119899
(119886119886119889119889minus119887119887)119899119899+1
4 119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894119900119900119875119875119900119900(119886119886119889119889 + 119887119887) = (minus1)119899119899minus1(119899119899minus1)119886119886119899119899
(119886119886119889119889+119887119887)119899119899
5 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119886119886119898119898119889119889 = 119898119898119899119899119886119886119898119898119889119889 (log119886119886)119899119899 6 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 119890119890119898119898119889119889 = 119898119898119899119899119890119890119898119898119889119889
7 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 sin(119886119886119889119889 + 119887119887) = 119886119886119899119899sin119886119886119889119889 + 119887119887 + 119899119899 1205871205872
8 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 cos(119886119886119889119889 + 119887119887) = 119886119886119899119899cos119886119886119889119889 + 119887119887 + 119899119899 1205871205872
9 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax sin(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 sin119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
10 119899119899119905119905ℎ 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890 119875119875119894119894 eax cos(119887119887119889119889 + 119888119888) = (1198861198862 + 1198871198872)1198991198992119890119890119886119886119889119889 cos119887119887119889119889 + 119888119888 +
119899119899119905119905119886119886119899119899minus1 119887119887119886119886
1
2
3
4
5
6
7
8
9
10
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Statement- if y=uv where u and v are function of x having derivative of nth order then
119889119889119899119899 = 1198991198991198621198620119906119906119899119899119875119875 + 1198991198991198621198621119906119906119899119899minus11198751198751 + 1198991198991198621198622119906119906119899119899minus21198751198752 + ⋯hellip hellip hellip +119899119899119862119862119875119875119906119906119899119899minus119875119875119875119875119875119875+ ⋯hellip hellip +119899119899119862119862119899119899 119906119906119875119875119899119899
119908119908ℎ119890119890119875119875119890119890 119904119904119906119906119894119894119894119894119894119894119889119889119890119890119904119904 119889119889119890119890119899119899119875119875119905119905119890119890 119905119905ℎ119890119890 119899119899119906119906119898119898119887119887119890119890119875119875 119875119875119894119894 119889119889119890119890119875119875119894119894119875119875119886119886119905119905119894119894119875119875119890119890119904119904
Example 1 119868119868119894119894 119889119889 = 119889119889119899119899 log 119889119889 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 119889119889119899119899+1 = 119899119899 119889119889
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2
119868119868119894119894 119889119889 = cos (119898119898 log119889119889)119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892119889119889119899119899+2 + (2119899119899 + 1)119889119889119889119889119899119899+1 + (1198981198982 + 1198991198992)119889119889119899119899 = 0
Leibnitzrsquos Theorem
Statement- if y=uv where u and v are function of x having derivative of nth order then
Example 1
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
LINK FOR REFERENCE
Leibnitzrsquos Theorem for successive differentiation
httpswwwyoutubecomwatchv=67uJGwsZz-Q
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
The Taylorrsquos series is named after the English mathematician Brook Taylor (1685ndash1731)
The Maclaurinrsquos series is named for the Scottish mathematician Colin Maclaurin(1698ndash1746)
This is despite the fact that the Maclaurinrsquos seriesis really just a special case of the Taylorrsquos series
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
APPLICATIONS OF TAYLORrsquoS AND MACLAURINrsquoS SERIES
Expressing the complicated functions in terms of simple polynomials
Complicated functions can be made smooth Differentiation of the such functions can be
done as often as we please In the field of Ordinary Differential Equations when
finding series solution to Differential Equations In the study of Partial Differential Equations
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
GENERAL TAYLORrsquoS SERIES
(I) Expressing f(x + h) in ascending integral powers of h
provided that all derivatives of f(x) are continuous and exist in the interval [x x+h]
(II) Expressing f(x) in ascending integral powers of (x ndash a)
119894119894(119889119889 + ℎ) = 119894119894(119889119889) + ℎ119894119894ʹ(119889119889) + ℎ2
2119894119894ˈʹ(119889119889) +
ℎ3
3119894119894ˈˈˈ(119889119889) + ⋯⋯
119894119894(119889119889) = 119894119894119886119886 + (119889119889 minus 119886119886)
= 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
GUIDELINES FOR FINDING TAYLOR SERIES
Expanding f(x) about x = aDifferentiate f(x) several timesEvaluate each derivative at x = aEvaluate
Substitute the above values in
119894119894(119889119889) = 119894119894(119886119886) + (119889119889 minus 119886119886)119894119894ʹ(119886119886) + (119889119889 minus 119886119886)2
2119894119894ˈʹ(119886119886) +
(119889119889 minus 119886119886)3
3119894119894ˈˈˈ(119886119886) + ⋯⋯
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Example
Find the Taylor series for f(x) = sin x at c = π4
f(x) = sin x
f rsquo(x) = cos x
f rsquorsquo(x) = - sin x
f rsquorsquorsquo(x) = - cos x
f(4)(x) = sinx
24 2
f π =
24 2
f π =
24 2
f π = minus
24 2
f π = minus
(4) 24 2
f π =
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Conthellip
( )2
0
( ) 2 2 2 2( ) ( ) ( ) 2 2 4 2 2 4 2 4
n nn
n
f x c x x xn n
π π πinfin
=
minus= + minus minus minus minus +
sdotsum
2 3 4
2 4 4 41 ( ) 2 4 2 3
x x xx
n
π π ππ
minus minus minus = + minus minus minus + +
2 3 42 2 2 2 2( ) ( ) ( ) ( ) 2 2 4 2 2 4 2 3 4 2 4 4
x x x xπ π π π= + minus minus minus minus minus + minus
sdot sdot sdot
( ) ( )
0
( ) ( )( ) ( )( ) ( )
n n nn
n
f x c f cf c f c x c x cn n
infin
=
minus= + minus + minus +sum
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
The Maclaurinrsquos series is simply the Taylorrsquos series about the point x = 0It is given by
119943119943(119961119961) = 119943119943(120782120782) + 119961119961119943119943ʹ(120782120782) + 119961119961120784120784
120784120784 119943119943ˈʹ(120782120782) +
119961119961120785120785
120785120785 119943119943ˈˈˈ(120782120782) + ⋯⋯
MACLAURINrsquoS SERIES
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Find the Maclaurinrsquos series for f(x) = ln(x2 + 1)2( ) ln( 1)f x x= + (0) 0f =
2
2( )1
xf xx
=+
(0) 0f =
2
2 2
2 2( )( 1)
xf xxminus
=+
(0) 2f =
2
2 3
4 ( 3)( )( 1)x xf xx
minus=
+(0) 0f =
4 2(4)
2 4
12( 6 1)( )( 1)x xf xx
minus + minus=
+
(4) (0) 12f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+
(5) (0) 0f =
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Conthellip0(0)f =0(0)f =2(0)f =
( 00)f =(4) (0 2) 1f = minus
4 2(5)
2 5
48 ( 10 5)( )( 1)
x x xf xxminus +
=+ (5) ( 00)f =
6 4 2(6)
2 6
240(5 15 15 1)( )( 1)
x x xf xx
minus minus + minus=
+
(6) (0 4) 2 0f =
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum
2 3 4 5 62 0 12 0 240 2
0 3 4 5 6
0 x x x x x= + + + + +minus
+
4 62 4
2 3x xx x= minus +
2 2
0
( 1)1
n n
n
xn
+infin
=
minus=
+sum
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Find the Taylor series for f(x) = endash2x at c = 0
f(x) = endash2x f(0) = 1
f rsquo(x) = -2endash2x f rsquo(0) = -2
f rsquorsquo(x) = 4endash2x f rsquorsquo(0) = 4
f rsquorsquorsquo(x) = -8endash2x f rsquorsquorsquo(0) = -8
f(4)(x) = 16endash2x f(4)(0) = 16
( ) ( )2
0
(0) (0)(0) (0) 2
n n nn
n
f x f ff f x x xn n
infin
=
= + + +sum2 34 8 21 2
2 3
n nx x xxn
= minus + minus + +
0
( 2 )
n
n
xn
infin
=
minus= sum
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
MACLAURINrsquoS SERIES
We defined
the nth Maclaurin polynomial for a function as
the nth Taylor polynomial for f about x = x0 as
nn
kn
k
k
xxn
xfxxxfxxxfxfxxk
xf )(
)()(2
)())(()()(
)(0
020
0
00
000
0 minus++minus+minus+=minussum=
nn
kn
k
k
xn
fxfxffxk
f
)0(2
)0()0()0(
)0( 2
0++++=sum
=
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
DERIVATION FOR MACLAURIN SERIES FOR
Derive the Maclaurin series
++++=32
132 xxxex
The Maclaurin series is simply the Taylor series about the point x=0
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5432
5432 hxfhxfhxfhxfhxfxfhxf
( ) ( ) ( ) ( ) ( ) ( ) ( ) +primeprimeprimeprimeprime+primeprimeprimeprime+primeprimeprime+primeprime+prime+=+5
04
03
02
00005432 hfhfhfhfhffhf
Example
xexe
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
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httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
DERIVATION (CONT)
22
Since xnxxx exfexfexfexf ==primeprime=prime= )( )( )( )( and
1)0( 0 == ef n
the Maclaurin series is then
3)(
2)()()()( 3
02
000 heheheehf +++=
3
12
11 32 hhh +++=
So
32
1)(32
++++=xxxxf
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Find the Maclaurin polynomial for f(x) = x cos x
f(x) = cos x f(0) = 1
f rsquo(x) = -sin x f rsquo(0) = 0
f rsquorsquo(x) = - cos x f rsquorsquo(0) = - 1
f rsquorsquorsquo(x) = sin x f rsquorsquorsquo(0) = 0
f(4)(x) = cos x f(4)(0) = 1( )
2(0) (0)cos (0) (0) 2
nnf fx f f x x x
n= + + +
2 441 0 0 2 4x x
= + minus minus +
2 1
0
( 1)(2 )
n n
n
xn
+infin
=
minus= sum
We find the Maclaurin polynomial cos x and multiply by x
2 4 6
1 2 4 6x x x
= minus + minus3 5 7
cos 2 4 6x x xx x x= minus + minus
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Find the Maclaurin polynomial for f(x) = sin 3x
f(x) = sin x f(0) = 0
f rsquo(x) = cos x f rsquo(0) = 1
f rsquorsquo(x) = - sin x f rsquorsquo(0) = 0
f rsquorsquorsquo(x) = - cos x f rsquorsquorsquo(0) = -1
f(4)(x) = sin x f(4)(0) = 0( )
2(0) (0)sin (0) (0) 2
nnf fx f f x x x
n= + + +
3
0 0 03xx= + + minus +
2 1
0
( 1) (3 )(2 1)
n n
n
xn
+infin
=
minus=
+sum
We find the Maclaurin polynomial sin x and replace x by 3x
3 5 7
3 5 7x x xx= minus + minus
3 5 73 3( ) ( ) ( )sin3 3 3 5 7
3
x x xxx = minus + minus
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Taylorrsquos amp Maclaurinrsquos Theorem for one variable
httpnptelacincourses12210401711
httpwwwcreativeworld9com201102iit-guest-lecture-mathematics-iii-videohtml
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
C
O A N
P(xy)
M
Y
X
Definition An asymptote of a curve is a line such that the distance between the curve and the line approaches zero as they tend to infinity In other words
A Straight line at a finite distance from the origin is said to be an asymptote of an infinite branch of a curve if the perpendicular distance of a point P on that branch from the straight line tends to zero as P tends to infinity along the branch of the curve
(Y) (P(xy))
(C) (M)
(N) (O) (A) (X)
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
A Curve With Finite Branches A Curve With Infinite BranchesEllipse Hyperbola
119961119961120784120784
119938119938120784120784+ 119962119962120784120784
119939119939120784120784= 120783120783 Its two branches are
y= b 120783120783 minus 119961119961120784120784
119938119938120784120784 and y= -b120783120783 minus 119961119961120784120784
119938119938120784120784
(upper half) (lower half) (Both branches lie within x=ax= -a y=b y=-b)
119961119961120784120784
119938119938120784120784minus119962119962120784120784
119939119939120784120784= 120783120783
Its infinite branches are
119962119962 = 119939119939119938119938radic119961119961120784120784 minus 119938119938120784120784 119962119962 = minus119939119939
119938119938radic119961119961120784120784 minus 119938119938120784120784
(Here 119962119962 rarr plusmninfin as 119961119961 rarr plusmninfin)
Its two branches are
y= b and y= -b
(upper half) (lower half)
(Both branches lie within x=ax= -a y=b
y=-b)
Its infinite branches are
(Here as )
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
KINDS OF ASYMPTOTES
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
ASYMPTOTE PARALLEL TO AXESAsymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892) minus 1198861198863(119889119889 + 119889119889)+ 1198861198864119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 6119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 11988911988921198891198892 minus 1198891198892119889119889 minus 1198891198891198891198892 + 119889119889 + 119889119889 + 1= 0 119860119860119904119904119898119898119901119901119905119905119875119875119905119905119890119890 119875119875119886119886119875119875119886119886119900119900119900119900119890119890119900119900 119905119905119875119875 119886119886119889119889119890119890119904119904
The equation of straight line y=mx+c is the oblique asymptote to the given curve
Oblique Asymptote
Asymptote Parallel to x-axis
Rule to find the asymptote || to X-axis is to equate to zero the real linear factors in the co-efficient of the highest power of x in the equation of the curve
Asymptote Parallel to y-axis
Rule to find the asymptote || to Y-axis is to equate to zero the real linear factors in the co-efficient of the highest power of y in the equation of the curve
The equation of straight line y=mx+c is the oblique asymptote to the given curve
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
WORKING RULE FOR FINDING OBLIQUE ASYMPTOTES OF AN ALGEBRAIC CURVE OF THE NTH DEGREE
1 Find the empty119899119899(119898119898) This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate empty119899119899(119898119898) to zero and solve for m Let its roots be m1m2m3helliphelliphellip
3 Find empty119899119899minus1(119898119898) by putting x=1 and y=m in the next lower terms of the equation Similarly empty119899119899minus2(119898119898) may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation 119888119888 = empty119899119899minus1(119898119898)
empty119899119899prime (119898119898)
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
1 Find the This can be obtained by putting x=1 y=m in the highest degree terms of the given equation of the curve
2 Equate to zero and solve for m
Let its roots be m1m2m3helliphelliphellip
3 Find by putting x=1 and y=m in the next lower terms of the equation Similarly may be found out by putting x=1 and y=m in the next lower degree terms in the curve and so on
4 Find the values of c1c2c3helliphelliphelliphelliphelliphellip corresponding to the values m1m2m3helliphelliphellipby using equation
5 Then the required asymptotes are y= m1x+c1 y= m2+c2helliphelliphelliphelliphelliphelliphellip
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
6 If empty119899119899prime (119898119898) = 0 119894119894119875119875119875119875 119904119904119875119875119898119898119890119890 119875119875119886119886119900119900119906119906119890119890 119875119875119894119894 119898119898 119886119886119899119899119889119889 empty119899119899minus1(119898119898) ne 0corressponding to that value then there will be no asymptote corresponding to that value of m
7 If empty119899119899prime (119898119898) = 0 and empty119899119899minus1(119898119898) ne 0 for some value of m the value of c are determined by
1198881198882
2empty119899119899primeprime (119898119898) + 119888119888empty119899119899minus1
prime (119898119898) + empty119899119899minus2(119898119898) = 0
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
6 If corressponding to that value then there will be no asymptote corresponding to that value of m
7 If and for some value of m the value of c are determined by
And this will determine two value of c and thus we shall have two parallel asymptotes corresponding to this value of m
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119865119865119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 (119889119889 minus 119889119889)2(119889119889 + 2119889119889 minus 1)= 3119889119889 + 119889119889 minus 7
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2119865119865119894119894119899119899119889119889 119886119886119900119900119900119900 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119905119905119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119888119888119906119906119875119875119875119875119890119890
(119894119894)1198891198892(119889119889 minus 2119886119886) = 1198891198893 minus 1198861198863
(119894119894119894119894)1198891198893 minus 21198891198891198891198892 minus 1198891198892119889119889 + 21198891198893 + 31198891198892 minus 7119889119889119889119889 + 21198891198892 + 2119889119889 + 2119889119889 + 1 = 0
(119894119894119894119894119894119894)1198891198893 minus 1198891198891198891198892 minus 1198891198892119889119889 + 1198891198893 + 1198891198892 minus 1198891198892 = 0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119888119888119906119906119875119875119875119875119890119890 11988911988921198891198892 minus 1198861198862(1198891198892 + 1198891198892)minus 1198861198863(119889119889 + 119889119889) + 1198861198864 = 0
Form the square through two of whose vertices the curve passes
Form the square through two of whose vertices the curve passes
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 1graphed on Cartesian coordinates
The x and y-axes are the asymptotes of the curve
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 2The graph of
y = x is the Asymptote
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 3The graph of x2 + y2 = (xy)2 with 2 horizontal and 2 vertical asymptotes
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 4The graph of
The y-axis (x = 0) and the line y = x are both asymptotes
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 5The graph of x3 + y3 = 3axy
A cubic curve the folium of Descartes (solid) with a single real asymptote (dashed) given by x + y + a = 0
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
PICTORIAL EXAMPLE 6The graph of Hyperbola
Its asymptotes are y = plusmn
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
ASYMPTOTE OF THE POLAR CURVES
119868119868119894119894 120572120572 119894119894119904119904 119886119886 119875119875119875119875119875119875119905119905 119875119875119894119894 119905119905ℎ119890119890 119890119890119890119890119906119906119886119886119905119905119894119894119875119875119899119899 119894119894(120579120579)= 0 119905119905ℎ119890119890119899119899 119875119875 sin(120579120579 minus 120572120572)
=1
119894119894prime(120572120572) 119894119894119904119904 119886119886119899119899 119886119886119904119904119889119889119898119898119901119901119875119875119905119905119890119890 119875119875119894119894 119905119905ℎ119890119890 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890
1119875119875
= 119894119894(120579120579)
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as 1119875119875
= 119894119894(120579120579)
2 Equate 119894119894(120579120579) to zero and solve for 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 3 Find 119894119894prime(120579120579) and calculate 119894119894prime(120579120579) at 120579120579 = 120579120579112057912057921205791205793 hellip hellip hellip hellip 4 Then write asymptote as 119875119875 sin(120579120579 minus 1205791205791) = 1
119894119894prime (1205791205791) 119875119875 sin(120579120579 minus 1205791205792) =
1119894119894prime (1205791205792)
helliphelliphelliphelliphelliphelliphelliphellip
Working rule for finding the asymptotes of polar curves
1 Write down the given equation as
2 Equate to zero and solve for
3 Find and calculate at
4 Then write asymptote as helliphelliphelliphelliphelliphelliphelliphellip
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
IMPORTANT FORMULAS1 119868119868119894119894 sin(120579120579) = 0 119905119905ℎ119890119890119899119899 120579120579 = 120587120587
4
2 119868119868119894119894119888119888119875119875119904119904120579120579 = 0 119905119905ℎ119890119890119899119899 120579120579 = (2119899119899 + 1) 1205871205872
3 119868119868119894119894119904119904119894119894119899119899120579120579 = 119904119904119894119894119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + (minus1)119899119899120572120572 4 119868119868119894119894119888119888119875119875119904119904120579120579 = 119888119888119875119875119904119904120572120572 119905119905ℎ119890119890119899119899 120579120579 = 2119899119899120587120587 plusmn 120572120572 119899119899 isin I 5 119868119868119894119894119905119905119886119886119899119899120579120579 = 119905119905119886119886119899119899120572120572 119905119905ℎ119890119890119899119899 120579120579 = 119899119899120587120587 + 120572120572 6 sin(119899119899120587120587 + 120579120579) = (minus1)119899119899 sin120579120579 7 cos(119899119899120587120587 + 120579120579) = (minus1)119899119899 cos120579120579 8 tan(119899119899120587120587 + 120579120579) = 119905119905119886119886119899119899 120579120579
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 119894119894119894119894119899119899119889119889 119905119905ℎ119890119890 119886119886119904119904119889119889119898119898119901119901119905119905119875119875119905119905119890119890119904119904 119875119875119894119894 119905119905ℎ119890119890 119894119894119875119875119900119900119900119900119875119875119908119908119894119894119899119899119900119900 119901119901119875119875119900119900119886119886119875119875 119888119888119906119906119875119875119875119875119890119890119904119904 (119894119894)119875119875 = 119886119886 tan120579120579 (119894119894119894119894)119875119875 sin120579120579 = 2 cos 2120579120579
1
2
3
4
5
6
7
8
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Derivative of a function
Single-Variable Function
Recall how we find the derivative for a Single Variable function f(x)
hxfhxf
dxdf
h
)()(lim0
minus+=
rarr
Rate of change of f with respect to x (slope)
Two-Variable Function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Partial derivatives of a function
x y
f(xy)
Rate of change of f with respect to xRate of change of f with respect to y
kyxfkyxf
yf
hyxfyhxf
xf
k
h
)()(lim
)()(lim
0
0
minus+=
partpart
minus+=
partpart
rarr
rarr
RemarksbullIt is called the Partial Derivativebecause it describes the derivative in one directionbullScripted ldquodrdquo not the regular ldquodrdquo or ldquo2rdquobullWhen differentiate f with respect to x we treat y as if y were a constant and vice versa
Partial Derivative of f with respect to xPartial Derivative of f with respect to y
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxyxyx
yx
xx
yxx
yxx
yxyyxxxx
f
+minus=
++minus=partpart
+partpart
+partpart
minuspartpart
=
++minuspartpart
=partpart
230)1()2(3
sup2)3()(sup2)(sup3)(
sup2)3sup2sup3(
2
2
xfpartpart Find HERE we treat ldquoyrdquo as a constant
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
If
find
Assignment
w = x2 minus xy + y2 + 2yz + 2z2 + z
partwpartx
partwparty
and partwpartz
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
46
Example A cellular phone company has the following production function for a certain product
where p is the number of units produced with x units of labor and y units of capital
a) Find the number of units produced with 125 units of labor and 64 units of capital
b) Find the marginal productivities of labor and of capital
c) Evaluate the marginal productivities at x = 125 and y = 64
p(x y) = 50x2 3y1 3
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
47
Higher-Order DerivativesSingle-Variable
Function
)derivative (3rd
)derivative (2nd
e)(derivativ
3
3
2
2
)(
)(
)(
dxfdxf
dxfdxf
dxdfxf
=
=
=
Multi-Variable Function
wrt x)f of derivative partial (3rd
wrt x)f of derivative partial (2nd
wrt x)f of derivative (partial
3
3
2
2
xff
xff
xff
xxx
xx
x
partpart
=
partpart
=
partpart
=
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Ex Given f(xy) = xsup3 - xsup2y + xy + 3ysup2
yxyxxff x +minus=partpart
= 23 2 found We
48
Find xxxxf
2
2
yf
partpart Find
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
49
( )
( )yxf
yf
xyfff
xyf
xf
yxfff
xxyyx
yyxxy
partpartpart
=partpart
partpart
=
partpart
==
partpartpart
=partpart
partpart
=
partpart
==
2
2
)(
)(
so yxxy ff =
Mixed Derivatives
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
If find the following partial derivatives
Assignment
z = f (x y) = x2y3 + x4 y + xey
=
=
=
===
yx
yy
y
xy
xx
x
ffffff
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x
and y if it can be expressed in the form 119889119889119899119899 empty119889119889119889119889 119875119875119875119875 119889119889119899119899 empty119889119889
119889119889
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
119894119894(119905119905119889119889 119905119905119889119889) = 119905119905119899119899119894119894(119889119889 119889119889)
For example if 119894119894(119889119889119889119889) = 119889119889+119889119889radic119889119889+radic119889119889
then
(119894119894) 119894119894(119889119889 119889119889) =119889119889(1 + 119889119889
119889119889)
radic119889119889(1 + 119889119889119889119889
= 11988911988912 empty
119889119889119889119889
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
119894119894(119889119889 119889119889 119911119911) = 119889119889119899119899empty 119889119889119911119911 119911119911119889119889 119875119875119875119875 119889119889119899119899(empty)
119889119889119889119889 119911119911119889119889 119875119875119875119875 119911119911119899119899empty
119889119889119911119911 119889119889119911119911
A Function f(xy) is said to be homogeneous of degree (or order) n in the variables x and y if it can be expressed in the form
An alternative test for a function f(xy) to be homogeneous of degree (or order ) n is that
For example if then
f(xy) is a homogeneous function of degree frac12 in x and y
Similarly a function f(xyz) is said to be homogeneous of degree n in the variables xyz if
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
=
119899119899119906119906
Since u is a homogeneous function of degree n in x and y it can be
expressed as 119906119906 = 119889119889119899119899 119894119894 119889119889119889119889
120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899minus1 119894119894119889119889119889119889 = 119889119889119899119899119894119894prime 119889119889119889119889 minus 1198891198891198891198892
119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899 119894119894 119889119889119889119889 minus 119889119889119899119899minus1 119889119889 119894119894prime 119889119889
119889119889 (119894119894)
119860119860119900119900119904119904119875119875 120597120597119906119906120597120597119889119889
= 119889119889119899119899 119894119894prime 119889119889119889119889
1119889119889
= 119889119889119899119899minus1119894119894prime 119889119889119889119889
119889119889120597120597119906119906120597120597119889119889
= 119889119889119899119899minus1 119889119889 119894119894prime 119889119889119889119889 (119894119894119894119894)
Alternative test is f(txtytz)= tn f(xyz)
Eulerrsquos Theorem on Homogeneous Functions
If u is a homogeneous function of degree n in x and y then
Since u is a homogeneous function of degree n in x and y it can be expressed as
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Adding (i) and (ii) we get 119889119889 120597120597119906119906120597120597119889119889
+ 119889119889 120597120597119906119906120597120597119889119889
= 119899119899119889119889119899119899119894119894 119889119889119889119889 = 119899119899119906119906
If u is a Homogeneous function of degree n in x and y then 1198891198892 12059712059721199061199061205971205971198891198892 +
2119889119889119889119889 1205971205972119906119906
120597120597119889119889120597120597119889119889+ 1198891198892 1205971205972119906119906
1205971205971198891198892 = 119899119899(119899119899 minus 1)119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119894119894119894119894 119906119906 sinminus1 119889119889 + 119889119889radic119889119889 + 119889119889
119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905 1198891198892 12059712059721199061199061205971205971198891198892 + 2119889119889119889119889
1205971205972119906119906 120597120597119889119889120597120597119889119889
+ 1198891198892 12059712059721199061199061205971205971198891198892 = minus
sin119906119906 cos 2119906119906 4 1198881198881198751198751199041199043119906119906
Composit functions
(119894119894)119894119894119894119894 119906119906 = 119894119894(119889119889119889119889) 119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119905119905)119889119889 = 120593120593(119905119905)
Then u is called a composit function of t and we can find dudt
(119894119894119894119894) 119894119894119894119894 119911119911 = 119894119894(119889119889119889119889)119908119908ℎ119890119890119875119875119890119890 119889119889 = empty(119906119906 119875119875)119889119889 = 120593120593(119906119906 119875119875)
Then z is called a composite function of u and v so that we can find 120597120597119911119911
120597120597119906119906 119886119886119899119899119889119889 120597120597119911119911 120597120597119875119875
Adding (i) and (ii) we get
If u is a Homogeneous function of degree n in x and y then
Composit functions
Then u is called a composit function of t and we can find dudt
Then z is called a composite function of u and v so that we can find
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and 119889119889119906119906
119889119889119905119905= 120597120597119906119906
120597120597119889119889 119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119905119905
+ 120597120597119906119906120597120597119911119911
119889119889119911119911119889119889119905119905
Cor 2 If z = f(xy) and x and y are the functions of u and v then
120597120597119911119911120597120597119906119906
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119906119906
120597120597119911119911120597120597119875119875
=120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
+ 120597120597119911119911120597120597119889119889
120597120597119889119889120597120597119875119875
Cor 3 If u=f(xy) where y= empty(119889119889) then since x = 120593120593(119889119889) u is a composite function of x
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
=gt119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 1 If u=f(xyz) and xyz are function of t then y is a composite function of t and
Cor 2 If z = f(xy) and x and y are the functions of u and v then
Cor 3 If u=f(xy) where y= then since x = u is a composite function of x
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
119889119889119906119906119889119889119889119889
= 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
But dudx=0 120597120597119906119906120597120597119889119889
+ 120597120597119906119906120597120597119889119889
119889119889119889119889119889119889119889119889
= 0 119875119875119875119875 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
= 0
119889119889119889119889119889119889119889119889
= minus 120597120597119894119894120597120597119889119889120597120597119894119894120597120597119889119889
= minus 119894119894119889119889119894119894119889119889
Hence the differential coefficient of f(xy) wrt x is 120597120597119894119894120597120597119889119889
+ 120597120597119894119894120597120597119889119889
119889119889119889119889119889119889119889119889
Cor 4 If we are given a implicit function f(xy) = c then u=f(xy) where u=c using cor 3 we have
But dudx=0
Hence the differential coefficient of f(xy) wrt x is
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Cor 5 If f(xy) = c then by cor 4 we have 119889119889119889119889119889119889119889119889
= minus 119894119894119889119889119894119894119889119889
119863119863119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119899119899119900119900 119886119886119900119900119886119886119894119894119899119899 119908119908 119875119875 119905119905 119889119889119908119908119890119890 119900119900119890119890119905119905
11988911988921199061199061198891198892119889119889
= minus 119894119894119889119889 119889119889119889119889119889119889 (119894119894119889119889) minus 119894119894119889119889
119889119889119889119889119889119889 119894119894119889119889
1198941198941198891198892= minus
119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 + 120597120597119894119894119889119889
120597120597119889119889 119889119889119889119889119889119889119889119889 minus 119894119894119889119889 120597120597119894119894119889119889120597120597119889119889 +
120597120597119894119894119889119889120597120597119889119889 119889119889119889119889119889119889119889119889
1198941198941198891198892
= minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
minus 119894119894119889119889 119894119894119889119889119889119889 minus 119894119894119889119889119889119889 119894119894119889119889119894119894119889119889
1198941198941198891198892
= minus1198941198941198891198891198891198891198941198941198891198892 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
119867119867119890119890119899119899119888119888119890119890 11988911988921198891198891198891198891198891198892 = minus
1198941198941198891198891198891198891198941198941198891198892 minus 2119894119894119889119889119894119894119889119889119894119894119889119889119889119889 minus 119894119894119889119889119889119889 1198941198941198891198892
1198941198941198891198893
Cor 5 If f(xy) = c then by cor 4 we have
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119911119911 = 21198891198891198891198892 minus 31198891198892119889119889 119886119886119899119899119889119889 119894119894 119894119894119899119899119888119888119875119875119890119890119886119886119904119904119890119890119904119904 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 2 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119908119908ℎ119890119890119899119899 119894119894119905119905
119901119901119886119886119904119904119904119904119890119890119904119904 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 3119888119888119898119898 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 119894119894119894119894 119889119889 119894119894119904119904 119901119901119886119886119904119904119904119904119894119894119899119899119900119900 119905119905ℎ119875119875119875119875119906119906119900119900ℎ 119905119905ℎ119890119890 119875119875119886119886119900119900119906119906119890119890 119889119889 = 1 119888119888119898119898
119889119889 119898119898119906119906119904119904119905119905 119887119887119890119890 119889119889119890119890119888119888119875119875119890119890119886119886119904119904119894119894119899119899119900119900 119886119886119905119905 119905119905ℎ119890119890 119875119875119886119886119905119905119890119890 119875119875119894119894 22
15 119888119888119898119898 119901119901119890119890119875119875 119904119904119890119890119888119888119875119875119899119899119889119889 119894119894119899119899 119875119875119875119875119889119889119890119890119875119875 119905119905ℎ119886119886119905119905 119911119911 119904119904ℎ119886119886119900119900119900119900 119875119875119890119890119898119898119886119886119894119894119899119899 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119894119894119894119894 119906119906 119894119894119904119904 119886119886 ℎ119875119875119898119898119875119875119900119900119890119890119899119899119890119890119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 119899119899119905119905ℎ 119889119889119890119890119900119900119875119875119890119890119890119890 119894119894119899119899 119889119889 119889119889 119911119911 119901119901119875119875119875119875119875119875119890119890 119905119905ℎ119886119886119905119905
119889119889120597120597119906119906120597120597119889119889
+ 119889119889120597120597119906119906120597120597119889119889
+ 119911119911120597120597119906119906120597120597119911119911
= 119899119899119906119906
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 3119865119865119894119894119899119899119889119889119889119889119889119889119889119889119889119889 119908119908ℎ119890119890119899119899
(119894119894) 119889119889119889119889 + 119889119889119889119889 = 119888119888 (119894119894119894119894) (cos 119889119889)119889119889 = (sin119889119889)119889119889
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Partial derivatives httpnptelacincourses12210100331
Partial derivatvesand euler th
wwwnptelacincourses122101003downloadsLecture-31pdf
NPTEL LINKS FOR REFERENCE
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
If u and v are functions of two independent variables x and y then the
determinant
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
is called Jacobian of uv with respect to xy and is
denoted by symbol J119906119906 119875119875119889119889 119889119889 119875119875119875119875 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
119869119869 119906119906 119875119875119908119908119889119889119889119889 119911119911
119875119875119875119875 120597120597(119906119906 119875119875119908119908)120597120597(119889119889119889119889 119911119911)
=
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119889119889
120597120597119906119906120597120597119911119911
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119889119889
120597120597119875119875120597120597119911119911
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119889119889
120597120597119908119908120597120597119911119911
If u and v are functions of two independent variables x and y then the determinant is called Jacobian of uv with respect to xy and is denoted by symbol J
Simolarly if uvw be the function of xyz then the Jacobian of uvw with respect to xyz is
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then 120597120597(119906119906 119875119875)120597120597(119889119889119889119889)
= 120597120597(119906119906 119875119875)120597120597(119875119875 119904119904)
120597120597(119875119875 119904119904)120597120597(119889119889119889119889)
[ 119888119888ℎ119886119886119894119894119899119899 119877119877119906119906119900119900119890119890 119894119894119875119875119875119875 119869119869119886119886119888119888119875119875119887119887119894119894119886119886119899119899119904119904]
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie 120597120597(119906119906 119875119875)
120597120597(119889119889 119889119889)= 120597120597(119889119889 119889119889)
120597120597(119906119906 119875119875)= 1
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1 119868119868119894119894 119889119889 = 119875119875 119904119904119894119894119899119899120579120579 119888119888119875119875119904119904empty 119911119911
= 119875119875 cos120579120579 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 120597120597(119889119889119889119889 119911119911)120597120597(119875119875120579120579120593120593)
= 1198751198752 sin120579120579
Properties of JACOBIANS
1 If uv are functions of rs where r s are functions of xy then
2 If J1 is the Jacobian of uv with respect to xy and J2 is the Jacobian of xy with respect to uv then J1J2 =1 ie
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
MAXIMA AND MINIMA OF FUNCTIONS OF TWO VARIABLES
A function f(xy) is said to have a maximum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
A function f(xy) is said to have a minimum value at x = a y = b if f(ab) f(a+hb+k) for small and independent values of h and k positive or negative
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
RULE TO FIND THE EXTREME VALUES OF A FUNCTION
Let z = f(xy) be a function of two variables(i) Find and(ii) Solve =0 and =0 simultaneouslyLet (ab) (cd)hellip Be the solutions of theseequations(iii) For each solution in step (ii) find r =s = t =
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
(iv) (a) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a maximum value at (ab)
(b) ) If rt - 0 and r 0 for a particular solution (ab) of step (ii)then z has a minimum value at (ab)
(c) If rt - 0 for a particular solution (ab) of step (ii)then z has no extreme value at (ab)
(d) If rt - =0 the case is doubtful and requires further investigation
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
ASSIGNMENT
1Examine the extreme values of + + 6 x + 12 2 Find the points on the surface = xy + 1 nearest to the
origin3 A rectangular box open at the top is to have a volume of
32 cc Find the dimensions of the box requiring least material for its construction
4 Divide 24 into three parts such that the continued product of the first square of the second and the cube of the third may be maximum
x2 y2
z2
z2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
Differentiation Under Integral SIGN
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and bint 119894119894(119889119889α)119889119889119889119889 119894119894119904119904 119886119886 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899 119875119875119894119894 α for example119887119887
119886119886
sinα dx = minuscosαα
0
1205871205872
= minus1αcos
1205871205872
α minus 11205871205872
0
= 1α
1 minus 1198881198881198751198751199041199041205871205872
α
119905119905ℎ119906119906119904119904 119894119894119899119899 119900119900119890119890119899119899119890119890119875119875119886119886119900119900 119894119894(119889119889α)119889119889119889119889 = 119865119865(α)119887119887
119886119886
If a function f(xα) of the two variables x and α α being called parameter be integrated wrt x between limits a and b
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2
119923119923119923119923119923119923119939119939119923119923119923119923119923119923119963119963prime119956119956 119929119929119929119929119929119929119923119923
119868119868119894119894 119894119894(119889119889α)119886119886119899119899119889119889 120597120597120597120597119889119889
[119894119894(119889119889α)]119887119887119890119890 119888119888119875119875119899119899119905119905119894119894119899119899119875119875119906119906119904119904 119894119894119906119906119899119899119888119888119905119905119894119894119875119875119899119899119904119904 119875119875119894119894 119889119889 119886119886119899119899119889119889 α then 119889119889119889119889α
119894119894(119889119889α)119889119889119889119889119887119887
119886119886
= 120597120597120597120597119889119889
[119894119894(119889119889α)] 119889119889119889119889 119908119908ℎ119890119890119875119875119890119890 119886119886 119886119886119899119899119889119889 119887119887 119886119886119875119875119890119890 119888119888119875119875119899119899119904119904119905119905119886119886119899119899119905119905119904119904 119894119894119899119899119889119889119890119890119901119901119890119890119899119899119889119889119890119890119899119899119905119905 119875119875119894119894 α119887119887
119886119886
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 1119864119864119875119875119886119886119900119900119906119906119886119886119905119905119890119890 tanminus1 119886119886119889119889119889119889(1 + 1198891198892) 119889119889119889119889 (119886119886 ge 0)119887119887119889119889 119886119886119901119901119901119901119900119900119889119889119894119894119899119899119900119900 119889119889119894119894119894119894119894119894119890119890119875119875119890119890119899119899119905119905119894119894119886119886119905119905119894119894119875119875119899119899 119906119906119899119899119889119889119890119890119875119875 119905119905ℎ119890119890 119868119868119899119899119905119905119890119890119900119900119875119875119886119886119900119900 119904119904119894119894119900119900119899119899infin
0
119864119864119889119889119886119886119898119898119901119901119900119900119890119890 2 119890119890119875119875119886119886119900119900119906119906119886119886119905119905119890119890 log(1 + 119886119886119889119889)
1 + 1198891198892 119889119889119889119889 119886119886119899119899119889119889 ℎ119890119890119899119899119888119888119890119890 119904119904ℎ119875119875119908119908 119905119905ℎ119886119886119905119905 log(1 + 119889119889)
1 + 1198891198892 1198891198891198891198891
0
119886119886
0
= 1205871205878
log 2