Pi Formula

Do you know the formula for calculating pi?

There are many, actually.   There is an easy one that I, Ada the Piphilologian thinks is best.

It is: Circumference over Width, C.O.W!!

Let's say there is a circle with 10 cm diameter.   So, its circumference is 10 x pi = 31.415926535... mooooo~, Ada might have to memorize lots of digits of pi to calculate circumference accurately!   Ada likes the simplicity for the pi formula, however, Ada must remind you that the famous C.O.W pi formula is only for circles!.