The radius of a sector is 21cm and it central angle is 120 . Find the perimeter of sector
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consider a full sphere of radius 21 cm.
what is the perimeter of that full circle?
it is 2 pi R
= 42pi
now, we know a full circle has an angle 360
so a sector having angle 120 is (120/360) of a complete circle right? ( I just took the ratio of the angle of sector to the angle of the sphere)
120/360 = 1/3
so sector = 1/3 x full circle
therefore perimeter or circumference of the sector = 1/3 x perimeter of circle
= 1/3 x 42pi
=14pi = 14 x 3.14 = 43.96 =44.0
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