Intermediate Algebra (6th Edition)

We know that a function is one-to-one if each x-value of the function corresponds to only one y-value and each y-value corresponds to only one x-value. The given function is a parabola. We can use the horizontal line test to determine if the function is one-to-one. If we insert a horizontal line at $y=0$, we will intersect the function more than once (at $x=0$ and $x=5$). Therefore, this function is not one-to-one.