Question

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In fig. two concentric circles with centre O ,have radii 21cm and 42 cm . If ∠AOB=60° find The area of shaded region .(Use π=
$\frac{22}{7}$
​

Answer 1

Given:

Radii of inner circle =21 cm=r

Radii of outer circle =42 cm=R

∠AOB=θ=60o

Area of ring =π(R2−r2)

Area of sector =360θπr2

The area of shaded region = Area of ring – Area of ABCD

= Area of ring – [Area of sector of outer circle – Area of sector of inner circle]

=π(R2−r2)−1π(R2−r2)×360θ

=π[R2−r2](1−360θ)

=722[422−212](1−36060)

=3465 cm

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Answer 2

Answer:

Given:

Radii of inner circle =21 cm=r

Radii of outer circle =42 cm=R

∠AOB=θ=60

o

Area of ring =π(R

2

−r

2

)

Area of sector =

360

θ

πr

2

The area of shaded region = Area of ring – Area of ABCD

= Area of ring – [Area of sector of outer circle – Area of sector of inner circle]

=

=3465 cm