Pi

The mathematical constant pi (π) is defined as the ratio of a circle's circumference to its diameter. It is also the ratio between a circle's area and its radius squared. It is approximately equal to 3.14159, but has been calculated to over one trillion digits.Pi Day: Celebrate Pi Day! Google Video: The Story of Pi;
Pi is also misspelled as pie.&pi is the Greek letter for "p"

Pi was approximated by the Babylonians over 4000 years ago. They measured it to be 3.125 according to a tablet dating back to approximately 1700 B.C..
In the Rhynd papirus (circa 1850 B.C.E.) there is a problem in which the scribe Ahmes affirms that the area of a circle of diameter d is the same as the area of a square of diameter 8/9d In other words, he tells that pi*(d/2)^2=pi*d^2/4 is the same as (8/9d)^2=64/81d^2 So he evaluates pi by 256/81=3.16049... while pi is 3.141... The error is 0.6% of the true value
Ancient mathematician Archimedes calculated pi by using the Pythagorean Theorem and by approximating the circle with inscribed and circumscribed regular polygons . By calculating up to a 96 sides polygon, he estimated pi to be between 3 1/7 and 3 10/71.
Despite the long available knowledge of the constant, a universal symbol was not used to describe it until the 1700s. William Jones was the first to use the symbol "π" in 1706. Leonhard Euler began using the symbol in 1737 after which it became popularized.ExplOratorium: A Brief History of π

• Amazon.com: Pi Books

• Amazon.com: Pi: A Source Book

• Amazon.com: Contact by Carl Sagan

• David Blatner: The Joy of Pi

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