2 In the diagram below, the radius of quadrant $O A D$ is 4 and the radius of quadrant $O B C$ is 8 . Given that $\angle C O D=30^{\circ}$, find the area of the shaded region $A B C D$.
(A) $12 \pi$
(B) $13 \pi$
(C) $15 \pi$
(D) $16 \pi$
(E) none of the above
2 Answer: (A)
Rotate $\triangle O A B 90^{\circ}$ anticlockwise about the point $O$ to overlap with $\triangle O D C$.
$\therefore$ Shaded area $=\frac{1}{4}(64 \pi-16 \pi)=12 \pi$.