## -1900 – pi

pi or π is a constant but irrational number that represents the ratio between the area of any circle and the square of its radius. This gives us the famous formula: area = π x r2, which can be approximated by 22/7 or 3.14159. pi can also be expressed by dividing the circumference of any circle by the diameter. pi is an irrational number, meaning that it cannot be represented by a fraction (or ratio) of two integers. The decimal representation of pi never ends and never repeats.

The first approximations of pi were recorded around -1900 in both Babylonia and Egypt. Archimedes invented a method to approximate pi using polygons drawn inside and outside a circle and increasing the number of sides on the polygons to approach the value of pi. Chinese mathematicians Liu Hui and Zu Chongzi demonstrated improved approximations. In the 1400s, an Indian mathematician named Madhava and a Persian mathematician named Jamshid pushed the number of digits in the approximation of pi to 11 and then 16. In 1949 ENIAC was used to calculate pi to over two thousand digits and current calculations can take it over a trillion digits.

Many forms of equations used in mathematics, geometry, trigonometry and physics use pi. Pi also is used in probability and statistics.

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