pi is an irrational number, that is the ratio of a circles circumference and its diameter. Irrational numbers cannot be written as p/q where p and q are integers. This means the decimal expansion of pi goes on forever and never repeats. 3.14 or 22/7 are approximations as are all decimal representations of pi. That is why the symbol is used to denote the exact value.

The first 20 decimals of pi are

3. 141592653 589793238 5

Generally a calculator will have a button labeled `pi` which is the greek letter for pi and will give you 8 decimal approximation to pi.

The symbol `pi` or the name pi was not used until the 17th century.

The Babylonians used 3 or 25/8 for pi 3800 years ago. The Egyptians sometimes used 256/81. Both are within 1% of the real value. Archimedes in the 2nd century BCE computed pi and found it's value somewhere between 220/71 and 22/7.

Pi is a transcendental number. It is irrational (cannot be expressed as a fraction -- a number of the form `p/q` where p,q are integers.) The fact that it is transcendental means that it cannot be expressed in finite form using only the operations +,-,x,/ and radicals. (It is not the solution to an algebraic equation, with the normal restrictive definition of an algebraic equation.) The decimal expansion for pi is nonrepeating and nonterminating.

`pi~~3.1415926`

`pi~~22/7`