Chapter 4 - An Introduction to Functions - 4-6 Formalizing Relations and Functions - Practice and Problem-Solving Exercises - Page 272: 24

This is not a function.

On the table, we see that x=3 is listed multiple times. One time, the corresponding y-value is -1, but the other time, the corresponding y-value is 1. Thus, because for one input (x-value) there are multiple outputs (y-values), this is not a function.