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The number π (/ p aɪ / ⓘ; spelled out as "pi") is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter.It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining π, to avoid relying on the definition of the length of a curve.
The table below is a brief chronology of computed numerical values of, or bounds on, the mathematical constant pi (π).For more detailed explanations for some of these calculations, see Approximations of π.
The constant π (pi) has a natural definition in Euclidean geometry as the ratio between the circumference and diameter of a circle. It may be found in many other places in mathematics: for example, the Gaussian integral, the complex roots of unity, and Cauchy distributions in probability. However, its ubiquity is not limited to pure mathematics.
A mathematical constant is a key number whose value is fixed by an unambiguous definition, often referred to by a symbol (e.g., an alphabet letter), or by mathematicians' names to facilitate using it across multiple mathematical problems. [1]
William Jones, FRS (1675 – 1 July 1749 [1]) was a Welsh mathematician best known for his use of the symbol π (the Greek letter Pi) to represent the ratio of the circumference of a circle to its diameter.
Approximations for the mathematical constant pi (π) in the history of mathematics reached an accuracy within 0.04% of the true value before the beginning of the Common Era. In Chinese mathematics, this was improved to approximations correct to what corresponds to about seven decimal digits by the 5th century.
where C is the circumference of a circle, d is the diameter, and r is the radius.More generally, = where L and w are, respectively, the perimeter and the width of any curve of constant width.
A History of Pi was originally published as A History of π in 1970 by Golem Press. This edition did not cover any approximations of π calculated after 1946. A second edition, printed in 1971, added material on the calculation of π by electronic computers, but still contained historical and mathematical errors, such as an incorrect proof that there exist infinitely many prime numbers. [4]