Pi is expressed by the Greek letter π (pronounced pài), which is a constant (approximately equal to 3. 14 1592653), 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 fractional part 3. 14 1592653 is enough for general calculation. Even if engineers or physicists want to make more accurate calculations, they only need to take the values to a few hundred decimal places at best.
Introduction to the origin of π:
π comes from the Greek π ε ρ φ ρ ε ρ α (periphery), which means edge and boundary. Although it existed as early as four ancient civilizations, π, as a cosmological constant, was really defined back to17th century.
From 65438 to 0748, the mathematician Euler defined and used π in his book Introduction to Infinitesimal Analysis, which really brought it into the understanding of mathematics. Perhaps because of its simple definition, π is ubiquitous in mathematical formulas, and its frequency and position in popular culture are much higher than other mathematical constants.