the area of two concentric circles are in ratio 4:9.the radious of outer circles is 21 cm.find radius of inner circle.
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r=14cm
The area of two concentric circle are 4:9
radius of big circle is 21cm
radius of small circle =?
so, area of big circle /area of small circle =22/7 r square /22/7 r square
9/4=21*21/r square
9r square =441*4
9 r square = 1764
r square = 1764/9
r square = 196
r = √196
r = 14cm
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