A semi-circle of radius 4cm has the same area as a complete circle of radius r cm. What is the radius of the complete circle?
posons r radius de semi circle
et r' radius de complete circle
on a : ( 2*r*pi ) / 2 = 2*r'*pi
r*pi = 2*r'*pi
r = 2r'
d'ou r = 4 cm =2r'
donc r' = 4/2 = 2
alors r' = 2
Area of semicircle: A1 = (1/2)*pi*4^2
Area of complete circle: A2 = pi*r^2
If A1 = A2 then pi *r^2 = (1/2)*pi*4^2
r^2 = (1/2)*16
r^2 = 8
r = sqrt(8) or r = 2*sqrt(2) cm
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