Solve the Formula for the Indicated Letter $$A = \frac { 1 } { 3 } \pi r ^ { 2 } \text { for } r$$

Multiple Choice

Solve the formula for the indicated letter. Assume that all variables represent nonnegative numbers.
- $$A = \frac { 1 } { 3 } \pi r ^ { 2 } \text { for } r$$

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