In figure 2, two concentric circles with centre O, have radii 21 cm and 42 cm. If ∠AOB = 60ׄ°, find the area of the shaded region. [Use π = 22/7
The area of a sector of a circle is given by,
A = πr2
where,
θ = centre angle in degrees
r = radius of the circle
A = area of the circle
⸫ Area of the shaded region = [Area of the outer circle] – [(Area of the minor sector of outer circle) + (Area of the major sector of inner circle)]
⸫ Area of the shaded region = πR2 – (πR2
+ πr2
)
= 
)
= 22 × 42 × 6 – (22 × 42 + 11 × 21 × 5)
= 5544 – 2079
= 3465 cm2
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