## Geometry: Common Core (15th Edition)

C) $r=\frac{1}{2}\sqrt{\frac{A}{\pi}}$
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. $\frac{1}{2}\sqrt{\frac{A}{\pi}}=r$