Pi in Greek letters? π (pronounced pài) is a constant, representing the ratio of circumference to diameter. It is an irrational number, that is, an infinite cycle decimal. In daily life, pi is usually expressed as 3. 14, which is used for approximate calculation.

The correlation is as follows:

Before π was used to refer to "pi", the Greek letter was used in the concept of geometry: 166. Starting from 1647, William Oughtred used π (Greek letters corresponding to P and D) to represent the ratio of the circumference and diameter of a circle in the Mathematical Keyboard.

William jones mentioned π in Introduction to Mathematics published in 1706. He was the first person to use the Greek letter π to express the ratio of a circle to its diameter. This Greek letter first appeared in the book when discussing a circle with a radius of 1, and mentioned "half its circumference (π)".

Jones chose π probably because it means "periphery" in Greek "π ε ρ η φ? The first word of ρ ε ι α ". However, Jones mentioned that his formula for π came from "the really clever Mr. John McKin", so people speculated that John McKin had used this Greek letter to express pi before Jones: 166.