$ \angle AOD=120{}^\circ . $ If the radius of the circle be r, then find the sum of the areas (in sq units) of quadrilaterals $ AODP $ and $ OBQC. $
A) $ \frac{\sqrt{3}}{2}r^{2} $
B) $ 3\sqrt{3}r^{2} $
C) $ \sqrt{3}r^{2} $
D) None of these
Correct Answer: C
$ \therefore $ $ \angle BOQ=\angle COQ=60{}^\circ $
$ \therefore $ $ \frac{SB}{OB}=\sin 60{}^\circ =\frac{\sqrt{3}}{2} $
$ \Rightarrow $ $ SB=\frac{r\sqrt{3}}{2} $
$ \therefore $ $ BC=2SB=r\sqrt{3} $ Area of quadrilateral $ BQCO=\frac{1}{2}\times BC\times OQ $ $ =\frac{1}{2}\times r\sqrt{3}\times r=\frac{r^{2}\sqrt{3}}{2} $ sq units
$ \therefore $ Sum of the areas of both quadrilaterals $ =2\times \frac{r^{3}\sqrt{3}}{2}=r^{2}\sqrt{3} $ sq units