Introductory Algebra for College Students (7th Edition)

$x=\left\{ -3,9 \right\}$
The left side of the given equation, $x^2-6x+9=36 ,$ is a perfect square trinomial whose factored form is \begin{array}{l}\require{cancel} (x-3)^2=36 .\end{array} Taking the square root of both sides (the Square Root Property), the solutions to the given equation are \begin{array}{l}\require{cancel} x-3=\pm\sqrt{36} \\\\ x-3=\pm\sqrt{(6)^2} \\\\ x-3=\pm6 \\\\ x=3\pm6 .\end{array} Hence, $x=\left\{ -3,9 \right\} .$