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Question
Find the circumference of the circle whose area is 25times the area of the circle with radius 7cm.
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Solution
The Area of a Circle with radius r = πr2
The Area of a Circle with radius7 = π(7)2
The Area of the bigger Circle
= 25 x π(7)2
= π(72 x 52)
= π(352)
Let radius of the bigger Circle = R
R2 = π(352)
⇒ radius of the bigger Circle = 35
The Circumference of a Circle with radius r = 2πr
The Circumference of a Circle with radiu 35r
= 2π x 35
= 220cm.
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