In the given figure, two concentric circles with centre O have radii 21 cm and 42 cm

• Mensuration (C10)

In the given figure, two concentric circles with centre O have radii 21 cm and 42 cm. If ∠AOB = 60°, find the area of the shaded region.  [Use π = 22/7]

Solution

Area of region ABDC = π × 60/360 (42² – 21²)

= 22/7 × 1/6 × 63 × 21

= 693 cm²

Area of shaded region = π(42² – 21²) – region ABDC

= 22/7 × 63 × 21 - 693

= 4158 – 693

= 3465 cm²