#### Celebrating math, Einstein, and pie – all on the same day

**■ Dennis Fletcher / Contributed**

Does 3.14 ring a bell? How about 3.14159? If you remembered the latter, you retained from junior high school the first six digits of an endless numerical constant called pi, represented by the lowercase Greek letter for pi (π). We learned that pi is used to represent the ratio of a circle’s circumference to its diameter.

We also learned, and some may still recall, the formula for calculating the circumference of a circle is C = πd. You multiply the value of pi (choose however long a form of the constant pi you want to use) times the diameter of the circle.

How is this information practical to the normal reader of this paper you ask? Assume for a moment that you just scored a great bargain on an old worn circular rug at your neighbor’s garage sale. When you got it home, you noticed that the edging was worn and frayed. Now you’d like to buy some new trim for it. Unfortunately, you only have a wooden yardstick hanging in one of those old hemp holders in the kitchen that says, “Yard by yard, life is hard … inch by inch, life’s a cinch.” Most of us inherited one of these from our Aunt Jenny years ago.

With our handy-dandy formula for the circumference of a circle, we can figure out the material we need. Simply measure between the two widest parts of the rug to get its diameter. Then multiply it by the value of pi to get the circumference.

Assume our recently-acquired treasure measures five feet in diameter. Then the circumference would be 5 X 3.14 feet = 15.7 feet. All accomplished without a clothier’s tape measure!

If we needed to know the actual area covered by that rug, then we would fall back on the area of a circle (actually a disk) which Aristotle gave us from ancient Greece: A = π r2. This says that the area covered by a circle is calculated by multiplying the value of pi times the square of the radius (the radius multiplied by itself). Since half the diameter is the radius, we would square the distance of 2.5 feet to get 6.25 feet and then multiply it by 3.14 to get 19.625 square feet of area. Simple!

The first highly accurate calculation of π was achieved by Archimedes of Syracuse (287–212 BC), one of the great mathematicians of the ancient world, in Measurement of a Circle written around 250 BC. Archimedes, the father of mathematics, approximated the area of a circle by using the Pythagorean Theorem cooked up by Pythagoras (c. 570 – c. 495 BC) on the ancient Greek island of Samos a good 250 years earlier.

Going back over 1000 years earlier, both the ancient Babylonians and Early Egyptians were hot on the trail of pi, being off by just a few hundredths of a point (Babylonians scored 3.125, Egyptians scored 3.1605 … thus, the Babylonians came in a close second, Egyptians a more distant third). The Ancient Hebrews thought it to be 3 (see 1 Kings 7:23 King James version).

**Pi Day (π Day)**

Why is this trip back into your long-forgotten algebra I class being dragged up over your morning coffee? Just to show you how much you may have forgotten? Heavens no. It’s because March 14 has come to be known as Pi Day.

The Exploratorium people in San Francisco thought up Pi Day in 1988, and it is now celebrated around the world and at most schools as a way of making mathematics more fun. It became an official U.S. holiday in March 2009. March 14, 2019 is the world’s 21st Pi Day.

March 14 is also Einstein’s birthday (b. 1879). So, his life has also been celebrated as part of π Day festivities.

If you Google Pi Day you will find such interesting sites as Piday.org that has pi resources, games, calculators and a quiz. The San Francisco Exploratorium has a fascinating site with lots of things for your kids or grandkids to do on Pi Day: https://www.exploratorium.edu/pi.

**Pi contest**

Pi has been calculated to at least 1.24 trillion places. Now here’s a pi-related question for puzzle lovers. Does the calculated area of a circle grow, even if only an infinitesimal amount, each time the value of pi is extended another digit for the calculation? Mail your answer to Dennis Fletcher c/o The Valley Chronicle or email editor@thevalleychronicle.com (put “Pi Day” as the subject). 3.14 winners (rounded down to 3) will be drawn one week later and each receive a Winner’s Certificate good for a fresh pie at Harvard Street Bakery and Tea Room.

The next time you look at a slice of pie, remember, when March 14 rolls around again, you can surprise your friends with the exclamation, “Well, you know it’s Pi Day!”