# Celebrating Pi on 3/14 and All Year Round!

On March 14, 2022 (3/14), we dug into whatever form of pi(e) we liked most (pizza, apple, chart—the range of possibilities is endless) in celebration of the mathematical constant π (pi). The date was chosen for the national day as 3, 1, and 4 are the first three significant figures of π. Larry Shaw, an employee of the San Francisco Exploratorium, first organized the celebration of the day in 1988, and on March 12, 2009, the US House of Representatives passed a non-binding resolution (HRES 224) recognizing March 14 as National Pi Day.

## A Slice of Background

A constant, sometimes also called a "mathematical constant," is any well-defined real number which is significantly interesting in some way. The constant pi is a real number defined as the ratio of a circle's circumference C to its diameter d = 2r,

pi = C/d

= C/(2r)

In other words, all the way around a circle divided by all the way across it. No matter how large or small the circle, its circumference is always π times its diameter.

The symbol π was devised by British mathematician William Jones in 1706 to represent the ratio and was later popularized by Swiss mathematician Leonhard Euler. The symbol derived from the first letter of the Greek word perimetros, meaning circumference. Its most elementary definition relates to the circle; therefore, π is found in many formulae in trigonometry and geometry, especially those concerning circles, ellipses, and spheres. And because pi is irrational (i.e., not equal to the ratio of any two whole numbers), its digits do not repeat, and an approximation, such as 3.14 or 22/7, is often used for everyday calculations. A decimal expansion of pi to 39 decimal places is: 3.141592653589793238462643383279502884197. . .

## How to Celebrate

For many, the question isn’t whether to celebrate Pi Day, but how. And the answers, much like the decimal places of pi, are limitless. Take the family out for a delicious pi-themed dinner (we’re thinking pizza, but no one’s going to argue with dessert for dinner, right?) And, if you’re able to plan in advance next year, some restaurants across the US even offer limited-time deals and promotions in celebration of Pi Day!

Or watch a handful of episodes of your favorite science fiction–themed television shows and see if you can catch a reference or two to the popular ratio. In fact, even non-science-y shows sometimes feature pi, such as The Simpsons! (We’re serious—check it out!)

If you head on over to the National Day Calendar page, you’ll find a list of notable events that have occurred on Pi Days of the past as well as a list of notable people who have called Pi Day their birthday. Or take a page out of NASA’s book, and explore pi the space way.

Looking for ways to incorporate pi in the classroom? Take a look at mathisfun.com, which offers multiple examples of ways pi can be helpful. No matter which way you slice it, March 14 will forever remain a day acknowledging the popular mathematical constant.

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