## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$(x-6)(x+6)$
The polynomial $x^2-36$ is a difference of the two squares $x^2$ and $6^2$. That is, by using the fact that $a^2-b^2=(a-b)(a+b)$, we have $$x^2-36=x^2-6^2=(x-6)(x+6) .$$