The diagonal of the largest square in a circle is the diameter of the circle:

D = 2r = 40cm cm

∴ Side length a=√2/2×40=20√2cm

∴S is positive =a? =800cm？

∫S circle =πr? =400πcm？

The area of a square is smaller than that of a circle;

(400π-800)/400π=(π-2)/π

That is, [100(π-2)/π]% is missing.

If π is 3. 14, it is about 36.3% less.