# Chapter 2 - Nonlinear Functions - 2.1 Properties of Functions - 2.1 Exercises: 4

$\boxed{\textbf{Not a function.}}$

#### Work Step by Step

A function is a rule that assigns to each element from one set exactly one element from another set. For the x-value of 9, TWO y-values are assigned (3 and -3), so this is $\boxed{\textbf{Not a function.}}$

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