1. The problem is to simplify or factor the expression $x^2 - 9$. 2. Recognize that $x^2 - 9$ is a difference of squares, which follows the formula $a^2 - b^2 = (a - b)(a + b)$. 3. Here, $a = x$ and $b = 3$ because $9 = 3^2$. 4. Applying the formula, we get: $$x^2 - 9 = (x - 3)(x + 3)$$ 5. This is the factored form of the expression. 6. Factoring helps to find roots or simplify expressions in algebra.