1. The problem is to find the zeros of the function $f(x) = x^2 - 9$. 2. The zeros of a function are the values of $x$ for which $f(x) = 0$. 3. Set the function equal to zero: $$x^2 - 9 = 0$$ 4. Use the difference of squares formula: $a^2 - b^2 = (a - b)(a + b)$. 5. Factor the equation: $$x^2 - 9 = (x - 3)(x + 3) = 0$$ 6. Set each factor equal to zero: $$x - 3 = 0 \quad \Rightarrow \quad x = 3$$ $$x + 3 = 0 \quad \Rightarrow \quad x = -3$$ 7. Therefore, the zeros of the function are $x = 3$ and $x = -3$. Final answer: $\boxed{3, -3}$