# How do you use the vertical line test to determine whether {(3,-1), (-2,3), (-1,-5), (3,2)} is a function?

Nov 6, 2016

By definition, in a function, there is only ONE y-value for each x-value.

The vertical line test is used if you have a graph, or if you have plotted the points. A vertical line has the equation $x = n$

If the line intersects the graph more than once, the graph is not a function.

In this case, when $x = 3$, there are two possible values for y.
$y = - 1$ OR $y = 2$ (there is a choice of y-values.)

Therefore these points do NOT represent a function.