Chapter 6 - Factoring, Solving Equations, and Problem Solving - 6.2 - Factoring the Difference of Two Squares - Problem Set 6.2 - Page 248: 13

$5(x+2)(x-2)$

Factoring out the greatest common factor of 5, the given expression, $ 5x^2-20 ,$ is equivalent to \begin{array}{l}\require{cancel} 5(x^2-4) .\end{array} Using $a^2-b^2=(a+b)(a-b)$, the completely factored form of the expression above is \begin{array}{l}\require{cancel} 5(x+2)(x-2) .\end{array}