In the diagram above, O is the center if the two concentric circle of radii 13cm and 10cm respectively. Find the area of the shaded portion in the sector with angle 1200 at the center
A.
\(\frac{1}{3}\pi cm^2\)
B.
\(\pi cm^2\)
C.
\(3\pi cm^2\)
D.
\(23\pi cm^2\)
E.
\(46\pi cm^2\)
Correct answer is D
\(\frac{120\pi}{360}(R^2 - r^2)\\
\frac{1}{3}\times \pi (13^2 - 10^2)\\
\frac{1}{3}\times \pi \times 69 = 23\pi cm^2\)