What you learnt about pi?

What you learnt about pi?
Pi is the sixteenth letter of the Greek alphabet and the abbreviation used to name a relationship, the ratio between the circumference of a circle and that circle’s diameter. As such, it is a mathematical constant. Pi allows you to find the circumference of the circle if you know the radius or diameter, and allows you to find the radius and diameter if you only know the circumference. The Greek form, π, is often used in mathematics and scientific settings.
The ancient Babylonians calculated the area of a circle by taking 3 times the square of its radius, which gave a value of pi = 3. One Babylonian tablet (ca. 1900–1680 BC) indicates a value of 3.125 for pi, which is a closer approximation.
The history of pi
Mathematicians began using the Greek letter π in the 1700s. Introduced by William Jones in 1706, use of the symbol was popularized by Euler, who adopted it in 1737. An 18th century French mathematician named Georges Buffon devised a way to calculate pi based on prob
Ability. You can try it yourself at the Exploratorium exhibit Throwing Pi.
In 1647, Oughtred used the symbol (d/Pi) for the ratio of the diameter of a circle to its circumference. In 1697, David Gregory used (Pi/r) for the ratio of the circumference of a circle to its radius. The first to use with its present meaning was an Welsh mathematician William Jones in 1706 when he states 3.14159 andc. = Pi. Euler adopted the symbol in 1737 and it quickly became a standard notation.
There are various other ways of finding the Lengths or Areas of particular Curve Lines, or Planes, which may very much facilitate the Practice; as for instance, in the Circle, the Diameter is to the Circumference as 1 to (16/5 - 4/239) - 1/3(16/5^3 - 4/239^3) + ... = 3.14159... (see A History of Mathematical Notation by Florian Cajori).
The modern symbol for pi was first used in our modern sense in 1706 by William Jones, who wrote:
Pi (rather than some other Greek letter like Alpha or Omega) was chosen as the letter to represent the number 3.141592... Because the letter Greek, pronounced like our letter 'p', stands for 'perimeter'.
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http://www.exploratorium.edu/pi/history_of_pi/index.html
http://egyptonline.tripod.com/history.htm
http://mathforum.org/dr.math/faq/faq.pi.html
http://egyptonline.tripod.com/history.htm