Answer
$p^6-25q^2$
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, $
(p^3-5q)(p^3+5q)
,$ simplifies to
\begin{array}{l}\require{cancel}
(p^3)^2-(5q)^2
\\\\=
p^6-25q^2
.\end{array}