User:Fredrik/Pi
From Wikipedia, the free encyclopedia
Pi or π is a mathematical constant, approximately equal to 3.14, that represents the ratio of any circle's circumference to its diameter in Euclidean geometry. The number also represents the ratio of a circle's area to the square of its radius, and appears in many other formulas from mathematics and geometry as well. Pi is an irrational number, which means that its decimal expansion 3.1415926535897932... never ends or repeats. 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.
- For the Greek letter, see pi (letter). For additional uses, see pi (disambiguation).
The Greek letter π, often spelled out pi in text, was adopted for the number from the Greek word for perimeter, probably by William Jones in 1706, and popularized by Leonhard Euler some years later. "π" is usually pronounced as pie when referring to the constant, although the letter is properly pronounced pee otherwise. The constant is occasionally also referred to as the circular constant, Archimedes' constant, or Ludolph's number.