## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

In order for the function to be one-to-one: For each value of $x$, there must be a unique $y$ value paired with it and every element of the domain (D) must be paired with a unique element of the range (R). We can see that for the value of $y=200$, there are two values of $x$; that is, $20$ and $25$ Therefore, the function is not a one-to-one function.