Answer
$x^2-64$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$ or the product of the sum and difference of like terms, the given expression, $
(x+8)(x-8)
$, is equivalent to
\begin{array}{l}\require{cancel}
(x)^2-(8)^2
\\\\=
x^2-64
.\end{array}