Answer
$r=\sqrt{\frac{A}{\pi}}$
Work Step by Step
To solve for r, isolate r on one side of the equation.
$A=\pi r^2$
Divide both sides by $\pi$.
$\frac{A}{\pi}=\frac{\pi r^2}{\pi}$
Simplify.
$\frac{A}{\pi}=r^2$
Take the square root of each side.
$\sqrt{\frac{A}{\pi}}=\sqrt{r^2}$
Simplify.
$\sqrt{\frac{A}{\pi}}=r$
