Choose the One Alternative That Best Completes the Statement or Answers

Multiple Choice

Choose the one alternative that best completes the statement or answers the question.
Solve the equation for the indicated variable. (Leave in your answer, when appropriate.)
- $A=\frac{1}{3} \pi r^{2}$ for $r$

A) $r=\frac{3 \pi}{A}$
B) $r= \pm \frac{\sqrt{3 \mathrm{~A} \pi}}{\pi}$
C) $\mathrm{r}=3 \sqrt{\mathrm{A} \pi}$
D) $r= \pm \frac{\sqrt{3 \mathrm{~A} \pi}}{3 \pi}$