Pi
Pi sounds like pie and is equal to about 3.1416. In math, this is the ratio of the circumference of a circle to its diameter. In other words, pi is a number that equals the quotient of the circumference of a circle divided by its diameter. Many people celebrate pi by holding a Pi Day on March 14th or 3/14.
The Greek letter pi represents the number by which the diameter of a circle must be multiplied to obtain the circumference. Pi is an irrational number. That is, it cannot be written as a simple fraction or as an exact decimal with a finite number of decimal places. However, you can increase the number of digits until you reach a number as near to pi as needed. Mathematicians with computers have calculated pi to millions of decimal places.
Pi is used in several mathematical calculations. The circumference of a circle can be found by multiplying the diameter by pi (c = pi X d). The area of a circle is yielded by multiplying pi by the radius squared (A = pi X r-squared). Pi is also used to calculate the area of a circle, and the volume of sphere or a cone.
The constant is named "π" because it is the first letter of the Greek words περιφέρεια 'periphery'[1] and περίμετρος 'perimeter', i.e. 'circumference'.
π is defined as the ratio of a circle's circumference to its diameter:
Circumference = π × diameter
Note that the ratio c/d does not depend on the size of the circle. For example, if a circle has twice the diameter d of another circle it will also have twice the circumference c, preserving the ratio c/d. This fact can also be stated as saying that all circles are similar.
Area of the circle = π × area of the shaded square
Alternatively π can be also defined as the ratio of a circle's area to the area of a square whose side is the radius:
The constant π may be defined in other ways that avoid the concepts of arc length and area, for example, as twice the smallest positive x for which cos(x) = 0.[2] The formulæ below illustrate other (equivalent) definitions.
Numerical value
The numerical value of π truncated to 50 decimal places is:
3.14159 26535 89793 23846 26433 83279 50288 41971 69399 37510
