## Intermediate Algebra (6th Edition)

$9x^8-4y^2$
Using the product of the sum and difference of like terms, $(a+b)(a-b)=a^2-b^2$, the given expression is equivalent to \begin{align*} & (3x^4+2y)(3x^4-2y) \\\\&= (3x^4)^2-(2y)^2 \\\\&= 9x^8-4y^2 .\end{align*}