Q14 of 78 Page 944

In the adjoining figure, the area enclosed between two concentric circles is 770 cm2 and the radius of the outer circle is 21 cm. Find the radius of the inner circle.


Given,


Outer radius of circle, R = 21 cm


Area of enclosed region = 770 cm2


Let the radius of inner circle be r.


Area of enclosed region = Area of outer circle – Area of inner circle


⇒ 770 = πR2 – πr2


⇒



⇒ 35(7) = (21)2 – r2


⇒ r2 = 441 – 245


⇒ r2 = 196


⇒ r = 14 cm


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