PI Day

For John, BLUF:  Fun with math.  Nothing to see here; just move along.

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This is the 13th of March.  In the United States it is 3 14, or the first three digits of the mathematical term PI—3.14.

Last year, 2015, it was 3 14 15, or the first five digits of PI, 3.1415.

Last year, for PI Day Mr Steven Strogatz wrote a sort article on PI for The New Yorker, "Why Pi Matters".

Here are the first three paragraphs:

Every March 14th, mathematicians like me are prodded out of our burrows like Punxsutawney Phil on Groundhog Day, blinking and bewildered by all the fuss. Yes, it’s Pi Day again.  And not just any Pi Day. They’re calling this the Pi Day of the century:  3.14.15.  Pi to five digits.  A once-in-a-lifetime thing.

I'm dreading it.  No hope of solving any equations that day, what with the pie-eating contests, the bickering over the merits of pi versus tau (pi times two), and the throwdowns over who can recite more digits of pi.  Just stay off the streets at 9:26:53, when the time will approximate pi to ten places:  3.141592653.

Pi does deserve a celebration, but for reasons that are rarely mentioned.  In high school, we all learned that pi is about circles.&in so; Pi is the ratio of a circle’s circumference (the distance around the circle, represented by the letter C) to its diameter (the distance across the circle at its widest point, represented by the letter d).  That ratio, which is about 3.14, also appears in the formula for the area inside the circle, A = πr2, where π is the Greek letter “pi” and r is the circle’s radius (the distance from center to rim).  We memorized these and similar formulas for the S.A.T.s and then never again used them, unless we happened to go into a technical field, or until our own kids took geometry.

Regards  —  Cliff