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1.2
Functions and Graphs
FunctionsDomains and RangesViewing and Interpreting GraphsEven Functions and Odd functions -
SymmetryFunctions Defined in PiecesAbsolute Value FunctionComposite Functions
…and why
Functions and graphs form the basis for understanding mathematics applications.
What you’ll learn about…
Functions
A rule that assigns to each element in one set a unique
element in another set is called a function. A function is like
a machine that assigns a unique output to every allowable
input. The inputs make up the domain of the function; the
outputs make up the range.
Function
A function from a set D to a set R is a rule that assigns a unique element in R to each element in D.
In this definition, D is the domain of the function and R is a set containing the range.
Function
( )
( )( )
The symbolic way to say " is a function of " is which is read as equals of .The notation gives a way to denote specific values of a function. The value of at can be written as , read
y x y f xy f x
f xf a f a
=
as " of ."f a
Example Functions
Evaluate the function ( ) 2 3 when = 6. f x x x= +
( )
( ) 2( ) 3
( ) 12 3
15
6 6
6
6
f
f
f
= +
= +
=
Domains and Ranges
( )When we define a function with a formula and the domain is
not stated explicitly or restricted by context, the domain is assumed to be
the largest set of -values for which the formula gives real
y f x
x
=
( )
-values -
the so-called natural domain. If we want to restrict the domain, we must say so.
The domain of 2 is restricted by context because the radius, ,
must always be positive.
y
C r r rp=
Domains and Ranges
The domain of 5 is assumed to be the entire set of real numbers.
If we want to restrict the domain of 5 to be only positive values,
we must write 5 , 0.
y x
y x
y x x
=
=
= >
Domains and Ranges
The domains and ranges of many real-valued functions of a real variable are intervals or combinations of intervals. The intervals may be open, closed or half-open, finite or infinite.
The endpoints of an interval make up the interval’s boundary and are called boundary points.
The remaining points make up the interval’s interior and are called interior points.
Domains and Ranges
Closed intervals contain their boundary points. Open intervals contain no boundary points
Domains and Ranges
Graph
( )( )
The points , in the plane whose coordinates are the
input-output pairs of a function make up the
function's .
x y
y f x
graph
=
Example Finding Domains and Ranges
2
Identify the domain and range and use a grapher
to graph the function .y x=
[-10, 10] by [-5, 15]
2y x=
( )
[ )
Domain: The function gives a real value of for every value of
so the domain is , .
Range: Every value of the domain, , gives a real, positive value of
so the range is 0, .
y x
x y
- ¥ ¥
¥
Viewing and Interpreting Graphs
Recognize that the graph is reasonable.
See all the important characteristics of the graph.
Interpret those characteristics.
Recognize grapher failure.
Graphing with a graphing calculator requires that you develop graph viewing skills.
Viewing and Interpreting Graphs
Being able to recognize that a graph is reasonable comes with experience. You need to know the basic functions, their graphs, and how changes in their equations affect the graphs.
Grapher failure occurs when the graph produced by a grapher is less than precise – or even incorrect – usually due to the limitations of the screen resolution of the grapher.
Example Viewing and Interpreting Graphs
2
Identify the domain and range and use a grapher to
graph the function 4y x= -
( ] [ )
Domain: The function gives a real value of for each value of 2
so the domain is , 2 2, .
Range: Every value of the domain, ,
gives a real, positive value of
so the range is [0, ).
y x
x
y
³
- ¥ - È ¥
¥
[-10, 10] by [-10, 10]
2 4y x= -
Even Functions and Odd Functions-Symmetry The graphs of even and odd functions have important
symmetry properties.
( )( ) ( )
A function ( )is a
if ( )
if
for every in the function's domain.
y f x
x f x f x
x f x f x
x
=
- =
- =-
even function of
odd function of
Even Functions and Odd Functions-Symmetry
The graph of an even function is symmetric about the y-axis. A point (x,y) lies on the graph if and only if the point (-x,y) lies on the graph.
The graph of an odd function is symmetric about the origin. A point (x,y) lies on the graph if and only if the point (-x,-y) lies on the graph.
Example Even Functions and Odd Functions-Symmetry
3Determine whether is even, odd or neither.y x x= -
( ) ( ) ( ) ( ) ( )
3
3 3 3
is odd because
x
y x x
f x xx x f xx x- -
= -
= - = - + = - - =--
3y x x= -
Example Even Functions and Odd Functions-Symmetry Determine whether 2 5 is even, odd or neither.y x= +
( ) ( ) ( )2 5 is neither because
2 5 2 5 ( )x x
y x
f x f x f x
= +
= + =- + ¹ ¹ -- -
2 5y x= +
Functions Defined in Pieces
While some functions are defined by single formulas, others are defined by applying different formulas to different parts of their domain.
These are called piecewise functions.
Example Graphing a Piecewise Defined Function
2
Use a grapher to graph the following piecewise function :
2 1 0( )
3 0
x xf x
x x
2 1; 0y x x= - £
2 3; 0y x x= + >
[-10, 10] by [-10, 10]
Absolute Value Functions
The absolute value function is defined piecewise by the formula
, 0
, 0
y x
x xx
x x
=
ì - <ïï= íï ³ïî
The function is even, and its graph is symmetric about the y-axis
Composite Functions
Suppose that some of the outputs of a function can be used as inputs of
a function . We can then link and to form a new function whose inputs
are inputs of and whose outputs are the numbers
g
f g f
x g ( )( )( )( ) ( )
.
We say that the function read of of is
. The usual standard notation for the composite is ,
which is read " of ."
f g x
f g x f g x
f g
f g
the composite
of and og f
Example Composite Functions
( )Given ( ) 2 3 and 5 , find .f x x g x x f g= - = o
( ) ( )( )( )( )
( )
2 3
1
5
5
0 3
g x
x
f g x
f
x
x
f=
=
= -
= -
o