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 Pi Math
What is Pi?
Pi (π) is a number that is roughly equal to 3.14159. Pi is the ratio of the circumference (perimeter) of any sized circle to its diameter. No matter what sized circle you have, the ratio of its circumference to its diameter is always the same -- pi. For example, when a circle's diameter is 1, its circumference is π. When a circle's diameter is 2, its circumference is 2 times π.

Pi is Irrational
Pi is an irrational number. This means that pi cannot be written as a fraction of two whole numbers and that the decimal digits of pi continue infinitely without any repeating pattern. Pi is roughly 3.14159265358979323846.... Using computers, pi has been calculated to many million of digits past the decimal point. For many purposes, using the approximation 3.1416 is sufficient. Good approximations for pi are 22/7 and 355/113.

Formulas
Pi is used in many calculations, including finding the circumference and area of a circle, and the volume and surface area of a sphere, cone, and cylinder. Pi is also used in geometry, probability and statistics, and many other fields.

 Circumference Area Circle(radius = r) 2π r π r2

Surface Area Volume Cylinder (radius = r, height = h) Sphere(radius = r) 4π r2 (4/3) π r3 2π r h (without the ends) π r2 h

The Name Pi
Mathematicians began using word pi (the Greek letter π) for this ratio in the early 1700s; the name pi was given to this number because p is short for perimeter.

Pi Day
Pi Day is a mathematical holiday celebrated by math classes on March 14th (3/14), with the peak celebration occuring at at 1:59 p.m (3/14 1:59). Pie, pizza, and other round foods are often served at Pi Day celebrations.

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