User:Gmac4247/basic-geometry/area-of-a-circle

Area of a circle
Comparing the area of a circle to the area of a square.

A=area of the square / circle

a=side of the square

r=radius of the circle

Using Pythagoras' theorem: $$ r=\sqrt{(a/4)^2 + (a/2)^2} $$ $$ r=\sqrt{1+4}*(a/4) $$ $$ A=16/5*r*r=3.2r^2 $$

References:

/perimeter-of-a-circle