## Precalculus (6th Edition)

The given relation does not define $y$ as a value of $x$. domain: $(-\infty, +\infty)$ range : $(-\infty, +\infty)$
RECALL: A function is a relation where every value of $x$ is paired with only one $y$ value. Substituting $0$ to $x$ gives: $x-y \lt 4 \\0-y \lt 4 \\-y \lt 4 \\y \gt -4$ This means when $x=0$, $y$ can be any real number greater than $-4$. Thus, when $x=0$, the points $(0, -3), (0, -2), (0, -1)$, plus a lot of others satisfy the inequality. An $x$ value is paired with more than one value of $y$, then the given relation does not define $y$ as a value of $x$. $x$ and $y$ can take any value therefore: domain: $(-\infty, +\infty)$ range : $(-\infty, +\infty)$