Answer
$x^{14}-4x^8+4x^6-16$
Work Step by Step
Using $(a+b)(c+d)=ac+ad+bc+bd$ or the product of 2 binomials, the product of the given expression, $
(x^6-4)(x^8+4)
,$ is
\begin{array}{l}\require{cancel}
x^6(x^8)+x^6(4)-4(x^8)-4(4)
\\\\=
x^{14}+4x^6-4x^8-16
\\\\=
x^{14}-4x^8+4x^6-16
.\end{array}
