The formula for the area of a circle is $\mathrm { A } = \pi r ^ { 2 }$, where $r$ is the radius. Solve the formula for $r$, and use your answer to find the radius of a circle with area 25 feet. Use $3.14$ for $\pi$ and round the answer to the nearest tenth of a foot.
A) $r = \frac { A } { 2 \pi } ; 4.0$ feet
B) $r = \sqrt { A - \pi } ; 4.7$ feet
C) $r = \sqrt { \frac { A } { \pi } } , r = - \sqrt { \frac { A } { \pi } } ; 2.8$ feet or $- 2.8$ feet
D) $r = \sqrt { \frac { A } { \pi } } ; 2.8$ feet

Question

Quizplus · Accepted Answer

To solve for $r$, you rearrange the formula to $r = \sqrt { \frac { A } { \pi } }$. For an area of 25 feet, $r = \sqrt { \frac { 25 } { 3.14 } } \approx 2.8$ feet. Negative radius doesn't apply to real-world circles, so only the positive value is correct.

The Formula for the Area of a Circle Is A=πr2\mathrm { A } = \pi r ^ { 2 }A=πr2

The Formula for the Area of a Circle Is $\mathrm { A } = \pi r ^ { 2 }$