pi

Given any circle, the ratio of the circumference to the diameter is an irrational number usually referred to as pi and denoted by the Greek letter \(\pi\).

Figure 1: The Definition of Pi

This ratio is the same regardless of the size of the circle, and is approximately 3.1415926. Pi is an irrational number, so its decimal representation cannot be finitely represented. Pi is also known to be a transcendental number, which means that it is not the solution of any strictly algebraic equation.