## Vertical Line Test.

A vertical line test is a test to example if it’s a function or not.

As we’ve seen the true nature of functions in the previous post, we can have a single output of y for its function x. For instance, take a look at image 01, where there’s a circle. For the horizontal x-axis, there are two outputs in the y-vertical axis, mathematically expressed as f(x). And when you get two or more outcomes for a single function, it’s not considered a function.

With that knowledge in mind, take a look at image 2 which represents the vertical line test. Vertical line test examines if it’s a function of not.

## A:

A is not a function, considering the fact that there are two outcomes found on the negative (left) side.

## B:

B is also not a function, considering the fact that there are two outcomes found on the negative (left) side.

## C:

C is a function, considering the fact that there is a single outcome found on either the positive or negative side.

## D:

D is also not a function, considering the fact that there are two outcomes found on either the positive or negative side.