Answer
$9(x+3)(x-3)$
Work Step by Step
Step 1: $9x^{2}-81$
Step 2: Both terms have a common factor of $9$, which is factored out:
$9x^{2}-81=9(x^{2}-9)$.
Step 3: $9(x^{2}-9)$ can be further factored into
$9(x^{2}-9)=9(x+3)(x-3)$.
Step 4: No further factorization possible.
