The result of the cos-1 function in the formula is in radians. Comparing a Circle to a Square It is interesting to compare the area of a circle to a square. The formula for the surface area of a sphere was first obtained by Archimedes in his work On the Sphere and Cylinder.
Since p is constant we need only the radius value from the user to calculate the area.
To find area of a circle with given value of radius use following formula. We use the following mathematical formula for calculating area and circumference of the circle In JavaScript. C2 2pir2 C2 4pi2r2 C2 4pipir2 As pir2 A C2 4piA Therefore. If a circle has radius r then the area of the circle is pi r2 pi being about 314159.