Answer
C) $r=\frac{1}{2}\sqrt{\frac{A}{\pi}}$
Work Step by Step
To solve for a variable, isolate that variable on one side of the equation.
$A=4\pi r^2$
Divide both sides by $4\pi$.
$\frac{A}{4\pi}=\frac{4\pi r^2}{4\pi}$
Simplify.
$\frac{A}{4\pi}=r^2$
Take the square root of each side.
$\sqrt{\frac{A}{4\pi}}=\sqrt{r^2}$
Simplify.
$\frac{1}{2}\sqrt{\frac{A}{\pi}}=r$
