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# Pi Day Facts

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## lib hist

on 9 March 2017

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#### Transcript of Pi Day Facts

Pi Day Facts
Pi has been calculated to more than a trillion digits…
Ages ago, Babylonian, Egyptian, Greek, Indian and Chinese mathematicians calculated pi to the first three or four places, and also used fractional approximations, including 22/7 and 355/113.
"In the 16th century, a German who presumably had a lot of time on his hands spent most of his life computing pi to 35 places," Devlin says.
A 19th-century Englishman made it to 707 places ... but only the first 527 were correct.
We've come a long way since then. Computers have been used to compute pi to well over a trillion places.

... but for most purposes, you don't need many digits at all.

Pi to just 9 places, for instance, allows you to calculate the circumference of the Earth and be accurate to within 1/4 of an inch.

Source
The symbol π is short for "perimeter."
"Pi is the circumference of a circle whose diameter is 1," says Devlin. A circumference is the perimeter of a circle — "and pi is the first letter of the Greek word perimeter."
And while pi may be ancient, that shorthand is not: the use of the symbol π to represent the value only dates back to the 18th century.

Pi can be calculated from an endless addition problem
A series known as Gregory's series consists of all the reciprocals of the odd numbers, summed up with alternating signs.
It might make more sense to see it. The endless sum begins: 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + 1/13 ... and continues infinitely.

It took Millennia to prove that pi is irrational