## College Algebra (10th Edition)

$\color{blue}{x=\left\{-3i, 3i\right\}}$
Take the square root of both sides: $\sqrt{x^2} = \pm \sqrt{-9} \\x=\pm \sqrt{-9} \\x=\pm \sqrt{9(-1)} \\x=\pm \sqrt{3^2(-1)} \\x=\pm 3\sqrt{-1}$ Note that $\sqrt{-1} = i$. Thus, the equation above simplifies to: $x=\pm 3i$ Therefore, the solutions are: $\color{blue}{x=\left\{-3i, 3i\right\}}$