Einstein was born, Hawking passes away and it’s Pi day…

# What is Pi?

Understanding pi is as easy as counting to one, two, 3.1415926535…

OK, we’ll be here for a while if we keep that up. Here’s what’s important: Pi (π) is the 16th letter of the Greek alphabet, and is used to represent the most widely known mathematical constant.

By definition, pi is the ratio of the circumference of a circle to its diameter. In other words, pi equals the circumference divided by the diameter (π = c/d). Conversely, the circumference of a circle is equal to pi times the diameter (c = πd).

Pi is an irrational number, which means that it is a real number that cannot be expressed by a simple fraction. That’s because pi is what mathematicians call an “infinite decimal” — after the decimal point, the digits go on forever and ever.

When starting off in math, students are introduced to pi as a value of 3.14 or 3.14159. Though it is an irrational number, some use rational expressions to estimate pi, like 22/7 of 333/106. (These rational expressions are only accurate to a couple of decimal places.)

While there is no exact value of pi, many mathematicians and math fans are interested in calculating pi to as many digits as possible.

Animation by Jacob Olsufka