Upload
lucy-watson
View
222
Download
3
Embed Size (px)
Citation preview
MATH 31 LESSONS
PreCalculus
1. Simplifying and Factoring Polynomials
A. Simplifying Polynomials
When you simplify a polynomial,
you are removing the brackets.
e.g.
(2x - 3) (4x + 1) = 8x2 - 10x - 3
Also, you are reducing a polynomial to the smallest
number of terms.
1. Adding and Subtracting Polynomials
You can add or subtract monomials
only with like terms.
e.g.
5x + 7x = 12x
11y2 - 7y2 = 4y2
6ab3 + 11ab3 = 17ab3
If they are not like terms,
then you cannot add them.
e.g.
2x + 3y
5y2 - 8y3
12xy2 + 8x2y
Ex. 1 Simplify 2x - 11y + 7x + 3y + 5x
Try this example on your own first.Then, check out the solution.
2x - 11y + 7x + 3y + 5xIdentify the like terms
2x - 11y + 7x + 3y + 5x
= 2x + 7x + 5x - 11y + 7yCollect the like terms
2x - 11y + 7x + 3y + 5x
= 2x + 7x + 5x - 11y + 3y
= 14x - 8y
2. Multiplying Polynomials
Monomial Monomial
Consider
5a2b3 10ab4 =
5a2b3 10ab4 = (5 10) (a2 a) (b3 b4)
Multiply numbers and like variables separately
5a2b3 10ab4 = (5 10) (a2 a) (b3 b4)
= 50 a3 b7
Monomial Polynomial
Consider
5x (6x - 7) =
5x (6x - 7) = 5x (6x) - 5x (7)
Multiply the monomial to each term of the polynomial
5x (6x - 7) = 5x (6x) - 5x (7)
= 30x2 - 35x
Binomial Binomial
Consider
(2x - 3) (4x + 1) =
(2x - 3) (4x + 1) = 2x (4x)
Use FOIL: First
(2x - 3) (4x + 1) = 2x (4x) + 2x (1)
Use FOIL: First
Outside
(2x - 3) (4x + 1) = 2x (4x) + 2x (1) - 3 (4x)
Use FOIL: First
OutsideInside
(2x - 3) (4x + 1) = 2x (4x) + 2x (1) - 3 (4x) - 3 (1)
Use FOIL: First
OutsideInsideLast
(2x - 3) (4x + 1) = 2x (4x) + 2x (1) - 3 (4x) - 3 (1)
= 8x2 + 2x - 12x - 3
= 8x2 - 10x - 3
Polynomial Polynomial
Consider
(x + 2y) (5x - 3y + 6) =
(x + 2y) (5x - 3y + 6) = x (5x) - x (3y) + x (6)
Multiply the first term to the entire polynomial
(x + 2y) (5x - 3y + 6) = x (5x) - x (3y) + x (6)
+ 2y (5x) - 2y (3y) + 2y (6)
Then, multiply the second term to the entire polynomial
(x + 2y) (5x - 3y + 6) = x (5x) - x (3y) + x (6)
+ 2y (5x) - 2y (3y) + 2y (6)
= 5x2 - 3xy + 6x + 10xy - 6y2 + 12y
= 5x2 + 6x + 7xy - 6y2 + 12y
Ex. 2 Simplify 2 (3a + 4) (5a - 6) - (2a - 7)2
Try this example on your own first.Then, check out the solution.
2 (3a + 4) (5a - 6) - (2a - 7)2
= 2 (3a + 4) (5a - 6) - (2a - 7) (2a - 7)
If it is a perfect square, then you should write both binomials. Then, you will remember to FOIL.
Notice:
(2a - 7)2 (2a)2 - (7)2
2 (3a + 4) (5a - 6) - (2a - 7)2
= 2 (3a + 4) (5a - 6) - (2a - 7) (2a - 7)
= 2 (15a2 - 18a + 20a - 24) - (4a2 - 14a - 14a + 49)
Be certain to show the brackets around the entire product
2 (3a + 4) (5a - 6) - (2a - 7)2
= 2 (3a + 4) (5a - 6) - (2a - 7) (2a - 7)
= 2 (15a2 - 18a + 20a - 24) - (4a2 - 14a - 14a + 49)
= 2 (15a2 + 2a - 24) - (4a2 - 28a + 49)
2 (3a + 4) (5a - 6) - (2a - 7)2
= 2 (3a + 4) (5a - 6) - (2a - 7) (2a - 7)
= 2 (15a2 - 18a + 20a - 24) - (4a2 - 14a - 14a + 49)
= 2 (15a2 + 2a - 24) - (4a2 - 28a + 49)
= 30a2 + 4a - 48 - 4a2 + 28a - 49
Distribute the negative to all terms
2 (3a + 4) (5a - 6) - (2a - 7)2
= 2 (3a + 4) (5a - 6) - (2a - 7) (2a - 7)
= 2 (15a2 - 18a + 20a - 24) - (4a2 - 14a - 14a + 49)
= 2 (15a2 + 2a - 24) - (4a2 - 28a + 49)
= 30a2 + 4a - 48 - 4a2 + 28a - 49
= 26a2 + 32a - 97 Add like terms
B. Factoring Polynomials
When you factor a polynomial,
you are adding brackets.
e.g.
8x2 - 10x - 3 = (2x - 3) (4x + 1)
You are making a polynomial into a product.
1. Greatest Common Factor (GCF)
The GCF is:
the largest number that divides evenly into
the coefficients
the smallest power of each variable
Taking out the GCF is usually the first step of factoring.
e.g.
Factor 12 x3 y4 + 18 x8 y2
12 x3 y4 + 18 x8 y2
= 6 x3 y2 (
The largest number that divides into 12 and 18 evenly
The smallest power of each variable
12 x3 y4 + 18 x8 y2
= 6 x3 y2 ( 2 x3-3 y4-2 + 3x8-3 y2-2 )
When you factor (divide), you subtract the exponents
12 x3 y4 + 18 x8 y2
= 6 x3 y2 ( 2 x3-3 y4-2 + 3x8-3 y2-2 )
= 6 x3 y2 ( 2 x0 y2 + 3x5 y0 )
= 6 x3 y2 ( 2 y2 + 3x5 )
2. Difference of Squares
Formula:
A2 - B2 = (A + B) (A - B)
Note:
There is no formula for A2 + B2.
e.g.
Factor 81 m8 - 16 y6 z4
81 m8 - 16 y6 z4
= (9 m4)2 - (4 y3 z2)2
Put into the form A2 - B2.
48 981 mmA 2346 416 zyzyB
81 m8 - 16 y6 z4
= (9 m4)2 - (4 y3 z2)2
= (9 m4 + 4 y3 z2) (9 m4 - 4 y3 z2)
A2 + B2 = (A + B) (A - B)
where A = 9 m4 and B = 4 y6 x2
3. Sum / Difference of Cubes
Formulas:
A3 - B3 = (A - B) (A2 + 2AB + B2)
A3 + B3 = (A + B) (A2 - 2AB + B2)
e.g. 1
Factor x3 - 64y3
x3 - 64y3
= (x)3 - (4 y)3
Put into the form A3 - B3
xxA 3 3
yyB 4643 3
x3 - 64y3
= (x)3 - (4 y)3
= (x - 4y) [ x2 + (x) (4y) + (4y)2 ]
A3 - B3 = (A - B) (A2 + AB + B2)
where A = x and B = 4y
x3 - 64y3
= (x)3 - (4 y)3
= (x - 4y) [ x2 + (x) (4y) + (4y)2 ]
= (x - 4y) (x2 + 4xy + 16y2)
e.g. 2
Factor 8x3 + 27y6
8x3 + 27y6
= (2x)3 + (3 y2)3
Put into the form A3 + B3
xxA 283 3
23 6 327 yyB
8x3 + 27y6
= (2x)3 + (3 y2)3
= (2x + 3y2) [ (2x)2 (2x) (3y2) + (3y2)2 ]
A3 + B3 = (A + B) (A2 - AB + B2)
where A = 2x and B = 3y2
8x3 + 27y6
= (2x)3 + (3 y2)3
= (2x + 3y2) [ (2x)2 (2x) (3y2) + (3y2)2 ]
= (2x + 3y2) (4x2 6xy2 + 9y4)
4. Grouping
When there are 4 terms, try grouping:
Group pairs of terms (you may need to rearrange)
Factor each pair
Factor out the common polynomial
e.g.
Factor ac bd + bc ad
ac bd + bc ad
No common factors for each pair.
Thus, we need to rearrange.
ac bd + bc ad
= ac ad + bc bd
ac bd + bc ad
= ac ad + bc bd
= a (c d) + b (c d)
They must have a common factor.
ac bd + bc ad
= ac ad + bc bd
= a (c d) + b (c d)
= (a + b) (c d)
5. Factoring Trinomials
Trinomials are polynomials with 3 terms.
They have the form
Ax2 + Bx + C = 0
We will deal with two cases:
Case 1: A = 1 (By inspection)
Case 2: A ≠ 1 (Decomposition)
Case 1: A = 1 (By inspection)
To factor x2 + Bx + C,
Find 2 numbers that add to B and multiply to C
Simply substitute the numbers into the two
binomial factors
e.g.
Factor x2 + 2x - 15
x2 + 2x - 15
Find two
numbers that ... add to 2
x2 + 2x - 15
Find two
numbers that ... add to 2 and multiply to -15
x2 + 2x - 15
2 numbers:
Sum = 2
Product = -155, -3
x2 + 2x - 15
2 numbers:
Sum = 2
Product = -15
= (x + 5) (x - 3)
Simply sub the numbers in
5, -3
Case 2: A ≠ 1 (Decomposition)
To factor Ax2 + Bx + C,
Find 2 numbers that add to B and multiply to AC
Replace B with these two numbers
Factor by grouping
e.g.
Factor 3x2 - 17x + 10
3x2 - 17x + 10
Find 2 numbers:
Sum = -17
3x2 - 17x + 10
Find 2 numbers:
Sum = -17
Product = 30
3x2 - 17x + 10
Find 2 numbers:
Sum = -17
Product = 30-15, -2
3x2 - 17x + 10
= 3x2 - 15x - 2x + 10Replace B with the two numbers, -2 and -15
3x2 - 17x + 10
= 3x2 - 15x - 2x + 10
= 3x (x - 5) - 2 (x - 5) Factor by grouping
3x2 - 17x + 10
= 3x2 - 15x - 2x + 10
= 3x (x - 5) - 2 (x - 5)
= (x - 5) (3x - 2)
Summary (Factoring methods)
GCF first
Look at the # of terms:
2 terms : - Difference of squares
- Sum / difference of cubes
3 terms: - Inspection (if A = 1)
- Decomposition (if A ≠ 1)
4 terms: - Grouping
Ex. 3
Factor 80 xy3 + 10xz6 completely.
Try this example on your own first.
Then, check out the solution.
80 xy3 + 10xz6
= 10x (8y3 + z6) Factor GCF first.
80 xy3 + 10xz6
= 10x (8y3 + z6)
Don’t stop here.
Do you see what else can be factored?
80 xy3 + 10xz6
= 10x (8y3 + z6)
= 10x [ (2y)3 + (z2)3 ] Sum of cubes
80 xy3 + 10xz6
= 10x (8y3 + z6)
= 10x [ (2y)3 + (z2)3 ]
= 10x (2y + z2) [ (2y)2 - (2y) (z2) + (x2)2 ]
80 xy3 + 10xz6
= 10x (8y3 + z6)
= 10x [ (2y)3 + (z2)3 ]
= 10x (2y + z2) [ (2y)2 - (2y) (z2) + (x2)2 ]
= 10x (2y + z2) (4y2 - 2yz2 + x4)
Ex. 4
Factor x2y - 54 + 6x2 - 9y completely.
Try this example on your own first.Then, check out the solution.
x2y - 54 + 6x2 - 9y
We will factor by grouping (4 terms).
However, we must rearrange so that there will be
common factors.
Can you see how?
x2y - 54 + 6x2 - 9y
= x2y - 9y + 6x2 - 54
This is one way to do so.
x2y - 54 + 6x2 - 9y
= x2y - 9y + 6x2 - 54
= y (x2 - 9) + 6 (x2 - 9)
x2y - 54 + 6x2 - 9y
= x2y - 9y + 6x2 - 54
= y (x2 - 9) + 6 (x2 - 9)
= (x2 - 9) (y + 6)
Don’t stop here.
Can you see what else can be factored?
x2y - 54 + 6x2 - 9y
= x2y - 9y + 6x2 - 54
= y (x2 - 9) + 6 (x2 - 9)
= (x2 - 9) (y + 6)
= (x + 3) (x - 3) (y + 6) Difference of squares
Ex. 5
Factor 3a4 - 7a2 - 20 completely.
Try this example on your own first.Then, check out the solution.
Notice that 3a4 - 7a2 - 20 is a trinomial.
To make it easier to factor, let’s do a substitution.
i.e.
Let x = a2
Then,
3 (a2)2 - 7 (a2) - 20 = 3x2 - 7x - 20
3x2 - 7x - 20
Find 2 numbers:
Sum = -7
Product = -60-12, 5
3x2 - 7x - 20
Find 2 numbers:
Sum = -7
Product = -60
= 3x2 - 12x + 5x - 20
-12, 5
3x2 - 7x - 20
Find 2 numbers:
Sum = -7
Product = -60
= 3x2 - 12x + 5x - 20
= 3x (x - 4) + 5 (x - 4)
-12, 5
3x2 - 7x - 20
Find 2 numbers:
Sum = -7
Product = -60
= 3x2 - 12x + 5x - 20
= 3x (x - 4) + 5 (x - 4)
= (x - 4) (3x + 5)
-12, 5
= (x - 4) (3x + 5)
Finally, we have to back-substitute x = a2:
= (x - 4) (3x + 5)
Finally, we have to back-substitute x = a2:
= (a2 - 4) (3a2 + 5)
Don’t stop here.
Do you see what else can be factored?
= (x - 4) (3x + 5)
Finally, we have to back-substitute x = a2:
= (a2 - 4) (3a2 + 5)
= (a + 2) (a - 2) (3a2 + 5)