Answer
$36r^4-1$
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 product of the given expression, $
(6r^2-1)(6r^2+1)
,$ is
\begin{array}{l}\require{cancel}
(6r^2)^2-(1)^2
\\\\=
36r^4-1
.\end{array}
