Answer
$64x^3-x$
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(8x+1)(8x-1)
,$ is equivalent to
\begin{array}{l}\require{cancel}
x[(8x)^2-(1)^2]
\\\\=
x(64x^2-1)
.\end{array}
Using the Distributive Property, the expression, $
x(64x^2-1)
,$ is equivalent to
\begin{array}{l}\require{cancel}
64x^3-x
.\end{array}