My Pi Day: A story of digits and pie crust

Should 3.14 be a national holiday?

Math teacher laments the quick passing of Pi Day.

Pi day, March 14th, has come and gone too quickly for those of us who are mathematicians, math teachers, and math enthusiasts. I think in a few more years it could get equal footing with President’s Day if Hallmark decides to throws its commercial weight behind the idea.

Pi Day brings back the whisperings around the dinner table of one of the few things you remember from your high school math class, along with those horrible memories of a train leaving Philadelphia at 1 p.m. and another train leaving Denver. (When did those two trains meet anyway?)

The morning after Pi Day I met with my parents at Perkins for dinner. They are proud of their math teacher son and I was proud of hosting a virtual classroom lecture on the history of pi. My mother, who remembers enough math to balance the checkbook, pleasantly surprised me.

“Pi-r-squared!” is the first thing she said when I asked if either of them knew what pi was. Yes indeed, she still had some high school math formulas in her head. The memorization had paid off, but only a little. She didn’t remember exactly what “pi-r-squared” meant. I reminded her that it was the formula for the area of a circle, if given the radius. That was a good segue into talking about what I covered in my online virtual lecture.

Since my audience was 4th grade and up I started with the basics. I used a picture of a pie (blueberry I think) and showed a red line going straight across the middle from one side to another, to illustrate the diameter. Then I showed how you can wrap that red line around the pie about three times, plus a little more. “Pi,” I said, “is how many times the diameter will wrap around a circle. It goes around one, two, three and .14159 dot dot dot.” That’s where we find out pi isn’t like a regular number.

The mathematical idea of pi has been around for thousands of years, along with many other things that make up geometry. That’s remarkable when you think about it. Geometry is very useful for building aqueducts, bridges, roads and palaces. The ancient Greeks and Romans didn’t actually needed pi to do those things. All they needed was a compass, a ruler, and some funding from the local governor.

But Archimedes of Syracuse (287 B.C.) was really interested in getting the exact value of pi. Why? Well, he was a major thinker of his day, and very philosophical about geometry. He made a good living inventing high-tech military weaponry when he wasn’t pondering circles. He used circles drawn inside regular polygons to estimate pi, and he eventually settled on it being somewhere between ²²³/₇₁ and ²²/₇ which is 3.141. Not bad considering he didn’t have algebra to work with. Algebra was still to be invented.

Various other math-a-holics took up the challenge and by the year 1600 a Dutch man named Van Ceulen calculated 35 digits. There still wasn’t an especially a pressing need to know the value of pi to such accuracy. It was fun to see how far they could go.  Perhaps it’s what they did instead of playing crosswords or Sudoku.

Carl Louis Ferdinand von Lindemann started pondering pi and contributed to the branch of math called number theory. Number theory is the math behind the numbers. (Never mind how you can use math to build a skyscraper.) Number theorists think about how prime numbers are like building blocks and they use them to build security systems, such as cryptography. von Lindemann determined that pi wasn’t “normal,” it was “transcendental,” meaning it doesn’t work as a solution to certain kinds of equations.

“Currently,” I said as I took a bite of my dessert, “the record number of digital of pi calculated was in 2002 by a Japanese mathematician named Kanada using a super computer. 1.24 trillion digits.”

As I finished my slice of pumpkin pie I noticed I had gone on a little too long about circles, famous mathematicians in history, and trillions of digits.

Too much of a good thing isn’t a good thing I reminded myself -- except on Pi Day. Now I’ll have to wait until next March 14th. In the meantime, I have some numbers to crunch, and some pie to eat.

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Andrew Borne is a high school math teacher in Minnesota.