inverse function Archives - Math and Multimedia

What is the horizontal line test?

August 19, 2015 GB High School Algebra, High School Mathematics

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

Suppose we have the function $f(x) = x^2$ . And we choose the number $y = 9$ which is in the range of $f$ . What number should we input in $f$ to get $9$ ? Well, we will have two numbers, those are $3$ and $-3$ . » Read more