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Question

Two circles touch each other externally. The sum of their area is 58 πcm2 and the distance between their center is 10 cm. Find the radii of the two circles.

A
7 cmand 3 cm
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B
5 cmand 7 cm
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C
3 cmand 2 cm
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D
None of these
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Solution

The correct option is A 7 cmand 3 cm
Let r be the radius of one circle and,
10r be the radius of other circle.
The area of the first circle is πr2
The area of the first circle is π(10r2)
Given,
The sum of these areas is 58πcm2
Therefore,
πr2+π(10r)2=58π
=>r2+(10r)2=58 [dividing both sides by π]
=>r2+(10)2+(r)22(10)(r)=58
=>r2+100+r220r=58
=>2r220r+42=0
=>r210r+21=0 [dividing both sides by 2]
=>r27r3r+21=0
=>r(r7)3(r7)=0
=>(r7)(r3)=0
r=3cm and r=7cm

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