Answer
$\left\{-6\sqrt{2},6\sqrt{2}\right\}$
Work Step by Step
In the form $x^2=c,$ the given equation, $
r^2-72=0
,$ is equivalent to
\begin{align*}
r^2=72
.\end{align*}
Taking the square root of both sides (Square Root Property), the equation above is equivalent to
\begin{align*}
r&=\pm\sqrt{72}
\\&=
\pm\sqrt{36\cdot2}
\\&=
\pm\sqrt{36}\cdot\sqrt{2}
\\&=
\pm6\sqrt{2}
.\end{align*}
Hence, the solution set of the equation $
r^2-72=0
$ is $\left\{-6\sqrt{2},6\sqrt{2}\right\}$.
