## Precalculus (6th Edition) Blitzer

RECALL: A function has every first component ($x$) paired with exactly one second component ($y$). Note that in the given equation, almost all $x$ values are paired with 2 different y-values. Example: When x=2: $y=\pm \sqrt{2^2-1} \\y=\pm \sqrt{4-1} \\y = \pm \sqrt{3}$ This means that the first component $x=2$, is paired with two second components: $y=\sqrt{3}$ and $y=-\sqrt{3}$. Therefore, the given equation is not a function.