Level:
Project ID:
2010012809
Source Problem:
Accepted:
0
Clonable:
1
Easy:
0
Which of the following formulas expresses the area of a regular pentagon inscribed in a circle of radius \( r \)? (See the picture.)
\( \frac{5r^2\sin72^{\circ}}2\)
\( \frac{10r^2\sin72^{\circ}}2\)
\( \frac{5r^2\sin36^{\circ}}2\)
\( \frac{5r \sin36^{\circ}}2\)