Maths(hope you can answer) ......

Pi or π is one of the most important mathematical constants, approximately equal to 3.14159. It represents the ratio of any circle's circumference to its diameter in Euclidean geometry, which is the same as the ratio of a circle's area to the square of its radius. Many formulas from mathematics, science, and engineering involve π.
It is an irrational number, which means that it cannot be expressed as a fraction m/n, where m and n are integers. Consequently its decimal representation never ends or repeats. Beyond being irrational, it is a transcendental number, which means that no finite sequence of algebraic operations on integers (powers, roots, sums, etc.) could ever produce it. Throughout the history of mathematics, much effort has been made to determine π more accurately and understand its nature; fascination with the number has even carried over into culture at large.
The Greek letter π, often spelled out pi in text, was adopted for the number from the Greek word for perimeter "περίμετρος", probably by William Jones in 1706, and popularized by Leonhard Euler some years later. The constant is occasionally also referred to as the circular constant, Archimedes' constant (not to be confused with an Archimedes number), or Ludolph's number.


圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Pi-unrolled-720.gif/360px-Pi-unrolled-720.gif



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
When a circle's diameter is 1, its circumference is π.


Fundamentals

The letter π


圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Pi-symbol.svg/180px-Pi-symbol.svg.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
Lower-case π (the lower case letter is used for the constant)


Main article: pi (letter)
The name of the Greek letter π is pi, and this spelling is used in typographical contexts where the Greek letter is not available or where its usage could be problematic. When referring to this constant, the symbol π is always pronounced like "pie" in English, the conventional English pronunciation of the letter. In Greek, the name of this letter is pronounced /pi/.