+122 The ancient Greek mathematicans,who were fascinated by the circle,discovered that if they measured the area of a circle and its radius they always got the same number if they divided the area by the square of the radius.They also discovered that they always got that self same number if they measured the diameter and divided it by twice the radius. They called this number pi. So you have the formulae Area=pi times r^2 and Diameter= 2pi times r.
(They measured the area of circles by drawing as many tiny squares as they could fit in,and then adding up all the areas of the squares.As you cannot fill a circle entirely with squares,no matter how small you make them,pi cannot be written as a finite number,and is called an irrational number.It has been calculated to hundreds of decimal places by NASA as pi crops up almost everywhere in maths and physics.) Hope this helps.
