Answer
$x\leq-3$ or $x\geq 3$
Work Step by Step
We know that the solution to the inequality:
$x^2\gt a$
Is equivalent to:
$x\lt -\sqrt{a}$ or $x\gt \sqrt{a}$
Therefore:
$x^{2}\geq 9$
$x\leq-\sqrt{9}$ or $x\geq\sqrt{9}$
$x\leq-3$ or $x\geq 3$