## Calculus with Applications (10th Edition)

$D = (-\infty, -3)\cup(3,+\infty)$
The domain of $f(x) = \log (x^{2} -9)$ consists of all x for which $x^{2} -9\gt 0$ Solving the inequality for x we have $x \lt -3$ or $x \gt 3$ $D = (-\infty, -3)\cup(3,+\infty)$