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Source: — Problem Solving |
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by Saffa » Wed Oct 01, 2008 1:42 am
You know the definition of the length of an arc and we know the radius of this circle = 9.

Thus circumference = 2*pi*9 = 18pi

Say T is the centre of the circle

ORP = 30 degrees so RPQ = 30 degrees

but PTR = 30 degrees (isoceles triangle PTR), thus the two angles TPQ and TQP both equal 70 degrees and angle PTQ equals 40 degrees (180 -70 -70)

Thus length = 18pi * 40/360 = 18pi * 1/9 = 2 pi

I'll try and draw it if need be3
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