Chapter 5 - Section 5.4 - Polynomials in Several Variables - Exercise Set - Page 376: 62

$49x^2y^4-100y^2$

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}