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If the small circle is r and the large one R, then the area of the small circle is half the area of the large circle when r=(R2/2)0.5
In this case R=10 so r=7.071
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I think it’s where Pi * 10^2 = 2 * Pi * r^2
Work out what r is.
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For any 2D shape, to reduce surface area by half, divide linear dimensions by square root of two.
gbj_tester
Jonny69
chez_jay
@moocher
I have a 10cm radius circle. I want to have another one inside it such that the area of the inner circle is equal to the area of the outer 'donut' section. Presumably it's not 5cm, but what is it?