(Q14)AB and CD are respectively arcs of two concentric circles of radii 21 cm. and 7 cm. with centre O (See figure). If ∠AOB = 30°, find the area of the shaded region. (use π).

Given , AB and CD are the arcs of two concentric circles

Radii of circles = 21 cm and 7 cm and ∠AOB = 30°

We know that,

Area of the sector =
x
360
 ×πr2

Area of the shaded region = Area of the OAB - Area of OCD

=
360
 ×
22
7
 ××  - 
30
360
 ×
22
7
 ××
=
1
 ×
22
7
 [ - ]
=
22
 × = .66cm2

Area of shaded region =.66 cm2