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 The circumference of the circle

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maths coordinator

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Posts : 113
Join date : 2010-01-28
Location : Deplomatic International School

PostSubject: The circumference of the circle   Fri Feb 12, 2010 8:48 am

Dear students,
Let's remember together.

Question
The radii of two circles are 19 cm and 9 cm respectively.
Find the radius of the circle which has circumference equal to the sum of the circumferences of the two circles.


Answer

Radius (r1) of 1st circle = 19 cm

Radius (r2) or 2nd circle = 9 cm

Let the radius of 3rd circle be r.

Circumference of 1st circle = 2πr1 = 2π (19) = 38π

Circumference of 2nd circle = 2πr2 = 2π (9) = 18π

Circumference of 3rd circle = 2πr

Given that, Basketball
Circumference of 3rd circle = Circumference of 1st circle + Circumference of 2nd circle

2πr = 38π + 18π = 56π

2nr =56n "dividing both sides by 2n"

r = 28

Therefore, the radius of the circle which has circumference equal to the sum of the circumference of the given two circles is 28 cm. Very Happy

Notice: n is not N , it is by 22/7 or 3.14 "the rule of circle cir. =2nr "
Maths coordinator sunny
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