Definition of a Function: For every “x” value there is only one “y” value
Given a Graph
Given an Order Pair
Domain and Range
Method
Method
Method
Use the Vertical Line Test
Use the definition of a function
Use the definition of a function
Draw light vertical lines through the graph. If
a line passes through more than one point
on the graph at the same time, then it is not
a function.
Examine the domain (x-values) of the order
pairs. If the same x-value appears with two
different y-values, then it is not a function.
2, 3,  4, 0, 2,  1, 0,  5
This is not a function because the x-value (2), is
paired to two different y-values (3 and -1)
Examine the domain (x-values). If an x is
pointing to two different y’s, then it is not a
function.
Domain
Range
–5
3
2
0
1
–4
–7
–2
This is not a function because the x value (1) is
pointing to two different y’s (3 and – 2)
The Academic Support Center at Daytona State College (Math 13 pg 1 of 1)