Answer
$(8x+9)(8x-9)$
Work Step by Step
If $a$ and $b$ are real numbers, we know that $a^{2}-b^{2}=(a+b)(a-b)$. In words, the difference of the squares of two terms factors as a product of a sum and a difference of those terms.
Therefore, we know that $64x^{2}-81=(8x+9)(8x-9)$. In this case, $a=8x$ and $b=9$.
