In figure, 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.
A diagram showing a large circle centered at O with diameter AB and diameter CD perpendicular to each other. A smaller circle is inscribed, centered on OD, with diameter OD. The radius of the large circle is 7 cm. The shaded region consists of two parts: the area of the smaller circle and the area of the large circle segment bounded by arc BC and radii OB and OC.