Chapter 6 - Factoring, Solving Equations, and Problem Solving - 6.2 - Factoring the Difference of Two Squares - Problem Set 6.2 - Page 248: 25

$4(3+x)(3-x)$

Factoring out the greatest common factor of 4, the given expression, $ 36-4x^2 ,$ is equivalent to \begin{array}{l}\require{cancel} 4(9-x^2) .\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} 4(3+x)(3-x) .\end{array}