## What is the horizontal line test?

In January of this year, we have discussed about the **vertical line test**. We have learned that if a vertical line intersect a graph more than once, then that graph is not a function. In this post, we learn about the horizontal line test and its relation to inverse functions.

Suppose we have a function . Then, we input and call the output . If we do things backward, suppose we have the number which is in the range of . What value should we input to to get ? Let’s have a more specific example.

Suppose we have the function . And we choose the number which is in the range of . What number should we input in to get ? Well, we will have two numbers, those are and . » Read more