how to compute the area of a circle

A=πr^2

The area of a circle is equal to the square of its radius, multiplied by pi. Pi being equal to 3.1415926.....

We know this equation works because (one way):

double integral {x^2 + y^2 <= r} 1 dxdy
= integral{0-2pi} integral{0-r} R dRdt
= integral{0-r} 2*pi*R dR
= pi*r^2

Take the radius r
Equation to find the area of the circle is (pi)rr

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