**pi | Definition, Symbol, Number, & Facts | Britannica**
https://www.britannica.com/science/pi-mathematics

pi, in mathematics, the ratio of the circumference of a circle to its diameter. Because pi is irrational (not equal to the ratio of any two whole numbers), its digits do not repeat, and an approximation such as 3.14 or 22/7 is often used for everyday calculations.

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