## Intermediate Algebra (12th Edition)

$x=\left\{ -3,3 \right\}$
$\bf{\text{Solution Outline:}}$ To solve the given equation, $-4x^2+36=0 ,$ simplify first by dividing both sides by $GCF.$ Then express the equation in $x^2=c$ form and get the square root of both sides (Square Root Principle). $\bf{\text{Solution Details:}}$ Dividing both sides by $-4$, the equation above is equivalent to \begin{array}{l}\require{cancel} x^2-9=0 \\\\ x^2=9 .\end{array} Taking the square root of both sides (Square Root Principle), the equation above is equivalent to \begin{array}{l}\require{cancel} x=\pm\sqrt{9} \\\\ x=\pm3 .\end{array} Hence, $x=\left\{ -3,3 \right\} .$