• March 14th is Pi Day!

3.141592653589793238462643383279502884197169399375
10582097494459230781640628620899862803482534211706
79821480865132823066470938446095505822317253594081...

Pi (ð) 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.

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.

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) 2ð r ð r2

 Surface Area Volume Sphere(radius = r) 4ð r2 (4/3) ð r3 Cylinder(radius = r, height = h) 2ð r h (without the ends) ð r2h

The Name Pi
Mathematicians began using the word pi (the Greek letter ð) 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).