Answer
$49x^2y^4-100y^2$
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 product of the given expression, $
(7xy^2-10y)(7xy^2+10y)
,$ is
\begin{array}{l}\require{cancel}
(7xy^2)^2-(10y)^2
\\\\=
49x^2y^4-100y^2
.\end{array}