# Chapter 1 - Speaking Mathematically - Exercise Set 1.3: 11

No, this relation is not a function, because it maps every value of $x$ in the domain to two values of $y$ in the codomain. This is evidenced by the fact that the graph of the function fails the vertical line test.

#### Work Step by Step

Note, for example, that if we let $x=4=y^{2}$, then either $y=2$ or $y=-2$. A function must map every value in the domain onto exactly one value in the codomain.

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