Chapter 9 - Section 9.1 - Solving Quadratic Equations by the Square Root Property - Exercise Set - Page 631: 22

$x=\{ -18,6 \}$

Taking the square root of both sides (the Square Root Property), the solutions to the given equation, $ (x+6)^2=144 ,$ are \begin{array}{l}\require{cancel} (x+6)=\pm\sqrt{144} \\\\ x+6=\pm\sqrt{(12)^2} \\\\ x+6=\pm12 \\\\ x=-6\pm12 .\end{array} Hence, $ x=\{ -18,6 \} .$