Concentric circles

There is given a circle K with a radius r = 8 cm. How large must a radius have a smaller concentric circle that divides the circle K into two parts with the same area?

Correct result:

r2 =  5.6569 cm


r=8 cm  S=π r2=3.1416 82201.0619 cm2  S2=S/2=201.0619/2100.531 cm2  S2=π r22  r2=S2/π=100.531/3.1416=4 2=5.6569 cm

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