Chapter 6 - Factoring, Solving Equations, and Problem Solving - 6.2 - Factoring the Difference of Two Squares - Problem Set 6.2 - Page 248: 38

$9(x+1)(x-1)$

Factoring out the greatest common factor of 9, the given expression, $ 9x^2-9 ,$ is equivalent to \begin{array}{l}\require{cancel} 9(x^2-1) .\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} 9(x+1)(x-1) .\end{array}