1. The problem is to factor the expression $x^2 - 9$. 2. Recognize that $x^2 - 9$ is a difference of squares since $9 = 3^2$. 3. Use the difference of squares formula: $$a^2 - b^2 = (a - b)(a + b)$$ 4. Here, $a = x$ and $b = 3$, so: $$x^2 - 9 = (x - 3)(x + 3)$$ 5. Therefore, the factored form of $x^2 - 9$ is $(x - 3)(x + 3)$.