Question

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

Answer 1

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.