Chapter 5 - Exponents and Polynomials - 5.3 - Multiplying Polynomials - Problem Set 5.3 - Page 208: 93

$4x^2-9y^2$

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