9. In Fig, AB and CD are two diameters of a circle (with centre O) perpendicular to each other and OD is the diameter of the smaller circle. If OA = 7 cm, find the area of the shaded region.
Firstly, area of the smaller circle is :
Now, area of :-
or
And, area of the bigger semicircle is :
Hence area of shaded region is :-
Therefore area of shaded region is 66.5 cm2.