Relations and Functions

Module 1 Lesson 1

What is a Relation?

A ________ is a set of ordered pairs.

When you group two or more points in a set, it is

referred to as a relation. When you want to show that a

set of points is a relation you list the points in _______.

For example, if I want to show that the points (-3,1) ;

(0, 2) ; (3, 3) ; & (6, 4) are a relation, it would be written

like this:

{(-3,1) ; (0, 2) ; (3, 3) ; (6, 4)}

Domain and Range

Each ordered pair has two parts, an x-value and a y-value.

The x-values of a given relation are called the______.

The ___-values of the relation are called theRange.

When you list the domain and range of arelation, you place each (the domain and the range) in a separate set of braces.

For Example,

1. List the domain and the range of the relation {(-3,1) ; (0, 2) ; (3, 3) ; (6, 4)}

Domain: { -3, 0, 3, 6} Range: _______

2. List the domain and the range of the relation {(-3,3) ; (0, 2) ; (3, 3) ; (6, 4) ; ( 7, 7)}

Domain: ________ Range: {3, 2, 4, 7}

Notice! Even though the number 3 is listed twice in the relation, you only note the number _____ when you list the

domain or range!

Finding Domain and Range from a graph

What is the domain?

The graph to the left is of y = x2, and we can

square any number we want.

This makes the domain __________.

On a graph, the domain corresponds to the ________ axis.  Since that is the case, we need to look to the left and right to see if there are any end points or holes in the graph to help us find our domain.

If the graph infinite to left and to the right, then the domain is represented by all real numbers.

If I plug any number into this

function, am I ever going to be

able to get a negative number

as a result? No!

The range of this function is

all positive numbers which is represented by y ≥ 0.

On a graph, the range corresponds to the vertical axis.  We need to look up and down to see if there are any end points or holes to help us find our range. If the graph keeps going up and down with no endpoint then the range is all real numbers.

However, this is not the case here. The graph does not ever go below the x-axis, never returning a negative range value.

What's the range?

What is a Function?A function is a relation that assigns each

______ only one x-value.

What does that mean? It means, in order for the

relation to be considered a function, there cannot be

any repeated values in the domain.

There are two ways to see if a relation is a function:

1. Vertical Line Test

2. _________

Using the Vertical Line Test

Use the vertical line test to check if the relation is a function only ifthe relation is already graphed.

1. Hold a straightedge (pen, ruler, etc) vertical to your graph. 2. Drag the straightedge from left

to right on the graph. 3. If the straightedge intersects

the graph once in each spot , then it is a function.

4. If the straightedge intersects thegraph more than once in any spot, it is not a function.

A _______!

Examples of the Vertical Line Test

Mappings

If the relation is not graphed, it is easier to use what is called a ________.

When you are creating a mapping of a relation, you draw two ______.

In one oval, list all the _______ values. In the other oval, list all the range values. Draw a line connecting the pairs of domain and range

values. If any domain value ‘maps’ to two different range

values, the relation is not a function.

It’s easier than it sounds

Example of a Mapping

Create a mapping of the following relation and state whether or not it is a function.

{(-3,1) ; (0, 2) ; (3, 3) ; (6, 4)}

Steps

1. Draw ovals

2. List domain

3. List range

4. Draw lines to connect

-3

0

3

6

1

2

3

4

This relation is a _______ because each x-value maps to only one y-value.

Another Mapping

Create a mapping of the following relation and state whether or not it is a function.

{(-1,2) ; (1, 2) ; (5, 3) ; (6, 8)}

-1

1

5

6

2

3

8

Notice that even

though there are

two 2’s in the

range, you only

list the 2 once.

This relation is a function because each x-value maps to only one y-value.

It is _____________ if two x-values go to the same y-value.

……….

Last Mapping

Create a mapping of the following relation and state whether or not it is a function.

{(-4,-1) ; (-4, 0) ; (5, 1) ; (3, 9)}

-4

5

3

-1

0

1

9

This relation is NOT a function because the (-4) maps to the (-1) & the (0).

It is ____________if one x-value goes to two different y-values.

……….

Make sure to list

the (-4) only once!

Vocabulary Review

Relation: Domain:. Range: Function:

Vertical Line Test:

Mapping:

Practice

Complete the following questions and check your answers on the next slide.

1. Identify the domain and range of the following relations: a. {(-4,-1) ; (-2, 2) ; (3, 1) ; (4, 2)}

b. {(0,-6) ; (1, 2) ; (7, -4) ; (1, 4)}

2. Graph the following relations and use the vertical line test to see if the relation is a function. Connect the pairs in the order given.

a. {(-3,-3) ; (0, 6) ; (3, -3)}

b. {(0,6) ; (3, 3) ; (0, 0)}

3. Use a mapping to see if the following relations are functions: a. {(-4,-1) ; (-2, 2) ; (3, 1) ; (4, 2)}

b. {(0,-6) ; (1, 2) ; (7, -4) ; (1, 4)}

Answers (you will need to hit the spacebar to pull up the next slide)

1a. Domain: {-4, -2, 3, 4} Range: {-2, 2, 1}

1b. Domain: {0, 1, 7} Range: {-6, 2, -4, 4}

2a. 2b.

3a. 3b.

Function Not a Function

-4

-2

3

4

-1

2

1

0

1

7

-6

2

-4

4

Function Not a Function

Function Notation

The equation that represents a function is called a _________.

A function rule is written with two variables, xand y.

It can also be written in function notation using f(x), where f(x) represent the y value.

F(x) is read as ‘_______________’ When you are given a function rule, you can

evaluate the function at a given domain value to findthe corresponding range value or vice versa.

How to Evaluate a Function Rule

To evaluate a function rule, substitute the

value in for x and solve for y.

Examples

Evaluate the given function rules for f(2) which is a read as let x = 2.

f(x)= x + 5 f(x)= 2x -1 f(x)= -x + 2y=(2)+ 5

y= 7

y=2(2)-1

y= 4 – 1

y= 3

y=-(2)+2

y= -2 + 2

y= 0

……….

When f(x) equals a number

You can also be asked to let y equal a number and then solve for x.

Examples

Evaluate the given function rules for f(x) =2 which is a read as let y = 2.

f(x)= x + 5 f(x)= 2x -1 f(x)= -x + 7 2= x + 5

x = ___

2 =2x -1

3 = 2x

x= ____

2= -x+7

-5= -x

x= ___

……….

Evaluating for multiple values

You can also be asked to find the rangevalues for a given ______or vice versa.

This is the same as before, but nowyou’re evaluating the same function rule formore than one number.

The values that you are substituting in are xvalues, so they are apart of the domain.

The values you are generating are y-values,so they are apart of the ______.

Example

Find the range values of the function for the given domain.

f(x) = -3x + 2 ; {-1, 0, 1, 2}

y = -3x + 2 y = -3x + 2 y = -3x + 2 y = -3x + 2 y = -3(-1) + 2 y = -3(0) + 2 y = -3(1) + 2 y = -3(2)

+ 2 y = 3 + 2 y = 0 + 2 y = -3 + 2 y = -6 +2 y = __ y = ___ y = ___ y = __

The range values for the given domain are { _________}.

Steps

1. Sub in each domain value in one @ a time.

2. Solve for y in each

3. List y values in braces.

Find the domain

Find the domain values of the function for the given the range values.

f(x) = 2x - 7 ; {-3, -2, 4}

y = 2x -7 y = 2x -7 y = 2x - 7 -3 = 2x - 7 -2 = 2x -7 4 = 2x - 7 4 = 2x 5 = 2x 11= 2x x= 2 x = 5/2 x= 11/2

The domain values for the given range are { _________}.

Practice

1. Find the range values of the function

for the given domain.

f(x) = 3x + 1 ; {-4, 0, 2}

2. Find the domain values of the function

for the given range.

f(x) = -2x + 3 ; {-5, -2, 6}Steps

1. Sub in each value in one @ a time.

2. Solve for the unknown in each

3. List results in braces.

Answers

y = 3x + 1

y = 3(-4) + 1

y = -12 + 1

y = -11

y = 3x + 1

y = 3(0) + 1

y = 0 + 1

y = 1

Ans. { -11, 1, 7}

y = 3x + 1

y = 3(2) + 1

y = 6 + 1

y = 7

y = -2x + 3

-5 = -2x + 3

-8 = -2x

x = 4

y = -2x + 3

-2 = -2x + 3

-5 = -2x

x = 5/2

Ans. {4, 5/2 , -3/2}

y = -2x + 3

6 = -2x + 3

3 = -2x

x = 3/-2

1.

2.