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The number 𝜏 or tau (/taʊ/, /tɔː/) is the mathematical constant equal to the ratio of a circle's circumference to its radius, approximately 6.28319. Equivalently, it is the number of radians in a turn, the circumference of the unit circle, and the period of the sine and cosine functions. 𝜏 is exactly two times the more well-known mathematical constant π, the ratio of a circle's circumference to its diameter. However, some mathematicians have advocated for the use of a single letter to represent 2π, stating that this value is more natural than π.[citation needed] Like π, 𝜏 is irrational, meaning it cannot be expressed as the quotient of two integers, and is transcendental, meaning it is not a solution to any nonzero polynomial with rational coefficients. However, its value can be expressed precisely using infinite series, integrals, or as the solution to equations involving trigonometric functions.[citation needed]
The value of 𝜏, to 50 decimal places, is: