# How do you use the vertical line test to determine whether {(-2,9), (3,9), (-0.5,9), (4,9)} is a function?

Nov 3, 2016

Find how many times a vertical line would intersect the graph.
It is once, so this is a function.

#### Explanation:

The vertical line test is used when you have a graph. If you draw a vertical line and it intersects the graph only once, it is the graph of a function.

This is because when you draw a vertical line, you are choosing a specific x-value and finding how many y-values are associated with it.

For a function, each and every x- value should have only ONE y-value.

In this case, you have a set of points.

The y-values are all the same, so they represent a horizontal line.(the line $y = 9$)

If you draw a vertical line it would intersect it only once.

Each x-value has only one y-value.

If you had a choice of y-values it would not be a function.