Answer
$(5x+2)(5x-2)$
Work Step by Step
Using the factoring of the difference of $2$ squares which is given by $a^2-b^2=(a+b)(a-b),$ the given $\text{
expression,
}$ $
25x^2-4
,$ is equivalent to
\begin{align*}
&
(5x)^2-(2)^2
\\&=
(5x+2)(5x-2)
.\end{align*}
