How the letter 'pi' came in mathematics?

Question

Is pi mean 22/7? If so, how circumference of the circle will be 2*22/7 if radius would be 1.

Answer 1

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.

Answer 2

$\pi \neq \frac{22}{7}$. 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.

• For more information about $\pi$ i would suggest you to read the wiki article: http://en.wikipedia.org/wiki/Pi

Answer 3

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.

Answer 4

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.