Chapter R - Section R.3 - Polynomials - R.3 Exercises - Page 29: 55

$16x^4-81$

Using $(a+b)(a-b)=a^2-b^2$ or the special product of the sum and difference of like terms, the product of the given expression, $ (2x+3)(2x-3)(4x^2-9) ,$ is \begin{array}{l}\require{cancel} [(2x+3)(2x-3)](4x^2-9) \\\\= [(2x)^2-(3)^2](4x^2-9) \\\\= (4x^2-9)(4x^2-9) \\\\= (4x^2)^2-(9)^2 \\\\= 16x^4-81 .\end{array}