Chapter 4 - An Introduction to Functions - 4-6 Formalizing Relations and Functions - Practice and Problem-Solving Exercises - Page 272: 26

An example is below.

x-value, y-value: 1, 37 2, 91 1, 46 3, 10 This is not a function, for x=1 has an output of both 37 and 46. Thus, because for one input (x-value) there are multiple outputs (y-values), this is not a function.