Answer
$4x^{2}-9$
Work Step by Step
The standard form of a polynomial is
$a_{n}x^{n}+a_{n}x^{n-1}+\cdots+a_{1}x+a_{0}$
(written in order, highest degree first. If a term is missing, it means that the coefficient is 0)
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Recognize a difference of squares $(A-B)(A+B)=A^{2}-B^{2}$.
$(2x+3)(2x-3)=(2x)^{2}-3^{2}$
= $4x^{2}-9$
(Or, apply the FOIL method)
