Answer
$10(x+3)(x-3)$
Work Step by Step
Factoring the $GCF=
10
,$ the given expression, $
10x^2-90
,$ is equivalent to
\begin{align*}
10(x^2-9)
.\end{align*}
Using the factoring of the difference of $2$ squares which is given by $a^2-b^2=(a+b)(a-b),$ the expression above is equivalent to
\begin{align*}
&
10[(x)^2-(3)^2]
\\&=
10[(x)^2-(3)^2]
\\&=
10[(x+3)(x-3)]
\\&=
10(x+3)(x-3)
.\end{align*}