Answer
$4a^2-1$
Work Step by Step
Using $(a+b)(a-b)=a^2-b^2$, or the special product of the sum and difference of like terms, the given expression, $
(2a-1)(2a+1)
,$ is equivalent to
\begin{align*}\require{cancel}
&
(2a)^2-(1)^2
\\&=
4a^2-1
.\end{align*}
Hence, the expression $(2a-1)(2a+1)$ is equivalent to $4a^2-1$.
