Chapter 4 - Polynomials - Test: Chapter 4 - Page 300: 40

$9x^{10}-y^2$

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, $ (3x^5-y)(3x^5+y) ,$ is \begin{array}{l}\require{cancel} (3x^5)^2-(y)^2 \\\\= 9x^{10}-y^2 .\end{array}