A mathematics teacher named William Jones is credited with first using the symbol ? in 1706 to represent the concept of the ratio between a circle's circumference and diameter. It had previously been illdefined.
Prior to Jones' usage of the ? symbol, the ratio of a circle's circumference and diameter was known as "the quantity which, when the diameter is multiplied by it, yields the circumference." William Jones first used the symbol in his book, "Synopsis Palmariorum Matheseos, or A New Introduction to the Mathematics." Jones believed, but could not prove, that pi was irrational. In 1761, Johann Lambert first proved that pi was an irrational number.
your fat mouth.
http://wiki.answers.com/Q/Who_invented_the_pi_char...

Pi was chosen as the letter to represent the number 3.141592. because the pi in Greek,
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Pi has been known for so long that it is quite untraceable. The first theoretical calculation seems to have been carried out by Archimedes of Syracuse.
http://www.kgbanswers.com/whoinventedpi/4884083

Hi: To answer your question you need to know what pi is : It is the ratio of a circle's circumference to it's diameter. it a constant number that never changes no matter how big or.
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