Pi is the ratio of a circle’s circumference to its diameter. Although it is a non-terminating, non-repeating number, the decimal approximation 3.14 and the fraction 22/7 are typically used to represent the irrational mathematical constant. The Greek letter **π**, was first used as the symbol for pi in 1706 by William Jones, but only became popular after it was adopted by Swiss mathematician Leonhard Euler in 1737. Since then, pi has been used in numerous formulas, such *A* = **π***r*^{2} (area of a circle), *V* = **π***r*^{2}*h *(volume of a cylinder), and SA = 4**π***r*^{2} (surface area of a sphere); pi has also been used to convert degrees to radians. For example, a 30° angle is equivalent to π/6.

Pi Day has been celebrated for 27 years. In 1988, physicist Larry Shaw organized a party in honor of pi at the San Francisco

Exploratorium where participants walked around one of the building’s circular areas eating pies, and thus began the unofficial celebration of pi. Twenty-one years later, the US House of Representatives resolved that March 14^{th} would be National Pi Day.

But this year’s celebration will be one of the best of all time! That’s because 3/14/15 at 9:26:53 a.m. and p.m., will display the first 10 digits of pi (truncated, of course)! How exciting!

So how can you celebrate? Many, like me, will wear apparel displaying pi, some will eat pie, and others may attempt to memorize as many digits of pi as they can. A group of friends may create the pi symbol using their bodies. Some may sing songs or write poems in honor of pi. Maybe I'll even honor pi by walking 3.14 miles.

Additionally, there are many instructional ways to celebrate pi. Although students may be familiar with pi, nothing brings mathematics to life more than exploration.

- Using In Search of Pi, students measure circumferences and diameters of several different circular objects, and then using the gathered data, students discover pi.
- In Finding the Area of a Sector, students research three websites to learn about the circumference of a circle and how to find the arc length of a sector.
- For a more direct approach, Area and Circumference of a Circle can be used to explain pi and how to use it to find the area and circumference of circular objects. Once students view the tutorial, they can then complete a short quiz to test their knowledge.

How will you celebrate Pi Day?

Be sure to check out these additional resources from Curriculum Pathways:

Math Stretch

Approximating **π **with Inverse Trigonometric Functions