# How the letter 'pi' came in mathematics?

Is $\pi$ mean $\cfrac {22}{7}$? If so, how circumference of the circle will be $2\times \cfrac{22}7$ if radius is $1$.

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-1 since it is obvious the person asking didn't search anything on the subject. –  Djaian Nov 2 '10 at 15:53
@Djaian, is it necessary that people must search before posting a question? –  anon Nov 2 '10 at 18:21
@anon: They can do better than this. @P. Gangamohan: The History of Mathematical Symbols –  endolith May 28 '11 at 4:27
The question has 4 answers with a total 14 upvotes , maybe we should consider upvoting the question. –  Tomarinator May 20 '12 at 14:08
@SauravTomar: I see no reason to upvote. In fact I did not downvote yet, so now I did. –  TMM May 20 '12 at 14:15

Citing Ed Sandifer preprint on L. Euler and the Basel Problem (that was published in Euler at 300: an appreciation).

“It is clear that I employ here the letter $\pi$ to indicate the number of Ludolf of Kuelen, $3.14159265$, etc.” By this time, Euler has been using p to denote that constant for several years, but the convention will take many years more before it is universally adopted.

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From Pi: A Biography of the World's Most Mysterious Number by Posamentier and Lehmann:

According to the well-known mathematics historian Florian Cajori (1859-1930), the symbol $\pi$ was first used in mathematics by William Oughtred (1575-1660) in 1652 when he referred to the ratio of the circumference of a circle to its diameter as $\frac{\pi}{\delta}$, where $\pi$ represented the periphery of a circle and $\delta$ represented the diameter...

In 1706 William Jones (1675-1749) published his book Synopsis palmariorum matheseos, in which he used $\pi$ to represent the ratio of the circumference of a circle to its diameter. This is believed to have been the first time that $\pi$ was used as it is defined today... But not until he [Leonhard Euler - A.R.] used the symbol $\pi$ in his famous book Introductio in analysin infinitorum did the use of $\pi$ to represent the ratio of the circumference of a circle to its diameter become widespread.

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Oh, I've answered the question in the title rather than those in the body. –  Andrey Rekalo Nov 2 '10 at 10:45

$\pi \neq \frac{22}{7}$. First of all $\frac{22}{7}$ is just an approximate value of $\pi$. Note that $\pi$ is irrational so it cannot be expressed in the form $\frac{p}{q}$ where $p$ and $q \neq 0$ are integers.

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@ Crasic and @Chandr: This was my first question posted. So, I am really sorry for confusion made by me. –  P. Gangamohan Nov 2 '10 at 10:36

According to wikipedia

"The constant is named "$\pi$" because "$\pi$" is the first letter of the Greek word περίμετρος (perimeter)..."

Questions that can be avoided with a quick look at a wikipedia article are typically frowned upon here.

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Odd, I've seen "perimetron" but not "perimetros". Maybe somebody fluent in Greek should chime in. –  Ｊ. Ｍ. Nov 2 '10 at 9:43
The Greek dictionaries in Perseus prefer περίμετρον. –  Yuval Filmus Nov 2 '10 at 20:54
In any case, I think the first letter is the one that matters :D –  crasic Nov 2 '10 at 21:38
In modern Greek, it's περίμετρος. For the word used in ancient times, I guess Perseus should be trusted more. –  ypercube Mar 14 '11 at 14:58