1. 4.8 Functions and Relations
Algebra
4.8 Functions and Relations

2. Functions and Relations
A relation is a set of ordered pairs
A function is a rule that establishes a relationship between two quantities, called the input and the output.
Input = x The collection of the x values is known as the domain.
Output = y. The collection of the y values is known as the range.

3. Function
The most important part of the function: every input has only one output. An x cannot have two y’s.
Examples: x y x y 1 2 1 5 2 4 1 7 3 4 2 8 4 5 3 9
Is this relation a function?
Is this relation a function?
Yes. Each input has
only one output.
No. The input 1 has
Two outputs 5 and 7.

4. A Birthday Example Imagine this relation:
Input = All the students at SRVHS
Output = The Birthday of that Student
Is this a function?

5. Let’s See Person Birthday Is this a function? Jessica Jones May 5th
Does each input have only one output?
Bob Boone June 21st
Similarly, does each person have only
one birthday?
Sally Smith Nov. 18th
Todd Thomas Nov. 18th
Since each input has only one output, then
this is a function.
Todd Thomas April 3rd
This would make this not a function because an
input (Todd Thomas) would have more than one
Output (Nov. 18th and April 3rd). This cannot happen.

6. What if the input were the days of the year and the output was the people who had that day as their birthday? Let’s try as a class.
People’s
B-Day
Date
Is this a function?
Jan. 1st Stu Sanders
Does each input have only one output?
Jan. 2nd Lyn Lewis
Similarly, does each date have only
one person celebrating that day as
their birthday?
Jan. 3rd John Jacobs
Jan. 3rd Sally Struthers
No. Since there is an input that has
more than one output, then this is
not a function.

7. Vertical Line Test
A relation is a function if its graph passes the vertical line test. All vertical lines must intersect the graph only once.
Are these functions? Do they pass the vertical line test?
Yes!
No!
No!
Yes!

8. Evaluate the Following Function in Function Notation
f(x) = 2x – 3 when x = -2
f(-2) = 2(-2) – 3
= -4 – 3
= -7

9. You try! Evaluate the Following Function in Function Notation…
f(x) = -7x – 3 when x = 4
f(4) = -7(4) – 3
= -28 – 3
= -31

10. Graphing a Function Graph f(x) = -1/2x + 4 Replace f(x) with y
Graph y = -1/2x + 4
(0, 4)

11. Is the relation a function? If yes, state the domain and range.x y
Yes, the relation is a function! 1 -2 2 -3
The domain is 1, 2, 3, and 4 3 -3 4 -5
The range is -2, -3, -3, -5

12. Find the Slope of the function f
f(2) = 4 ; f(-1) = 10
These points are (2, 4) and (-1, 10)
Slope = 10 – 4
-1 – 2
= 6 -3
= -2

13. HW
P #11-23, 37-45