Level:
Project ID:
1003021603
Source Problem:
Accepted:
1
Clonable:
1
Easy:
0
Which of the following formulas expresses the area of a regular decagon inscribed in a circle of radius \( r \)? (See the picture.)
\( 10r^2\sin18^{\circ}\cos18^{\circ} \)
\( 10r^2\sin36^{\circ}\cos36^{\circ} \)
\( 5r^2\sin36^{\circ} \)
\( 5r^2\sin18^{\circ} \)