Chapter 4 - An Introduction to Functions - 4-6 Formalizing Relations and Functions - Practice and Problem-Solving Exercises - Page 272: 33

This is not a function.

We see that for the x-value, c, there are three different outputs. For one point, we see that c equals e, but for a different point, c equals d, and at another point, c equals b. Thus, this is not a function.