In Fig. 12.27, 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.
Radius (r1) of larger circle = 7 cm
Radius (r2) of smaller circle = 
cm
Area of smaller circle = 
r22
= 
* 
* 
= 
cm2
Area of semi-circle AECFB of larger circle = 
r12
= 
* 
* (7)2
= 77 cm2
Area of triangle ABC = 
* AB * OC
= 
* 14 * 7
= 49 cm2
Area of the shaded region
= Area of smaller circle + Area of semi-circle AECFB - Area of ΔABC
= 
+ 77 – 49
= 28 + 
= 28 + 38.5
= 66.5 cm2
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