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# Happy Pi Day!

In case you didn’t know, Saturday, March 14 (or 3/14), is Pi Day, a day set aside to celebrate and recognize the mathematical value of pi (π). March 14 is the day since pi is usually approximated by 3.14. In 2009, the U.S. House of Representatives officially appointed this day to acknowledge the importance of this value. It is usually approximated to more digits with 3.14159 being the most common, but you can carry it out to as many as you like since, being an irrational number, pi never ends. This year is special as the celebration is said to occur on 3/14/15 at 9:26:53 a.m. in honor of the value 3.141592653. A moment of silence at that time, please.

As you know, pi is a special and important value widely used in mathematics, science, and engineering. As a college graduate and engineer, you have used pi more times than you can remember. I remember approximating it on a slide rule in college, but today pi has its own button on every scientific calculator.

Pi is the value of the circumference of a circle (C) divided by its diameter (D) or π = C/D. It is widely used to calculate the area (A) of a circle (A = πR2) from its radius (R) and the volume of a cylinder of height H (V = πR2H). But I am sure you guys better remember formulas like v = Vsin2πft or XL = 2πfL or f = 1/2π√LC. Remember too, angular velocity is ω = 2πf. Also remember that a sine wave contains 2π radians. How could you ever forget?  Or how about the free-space Friis formula for wireless propagation:

Pr = PtGtGrλ2/16π2d2

Remember that?

An old joke from engineering school: One engineer to another: “Say something to me in mathematics.”  The other engineer says “pi R square.”  The other engineer says, “No, pie are round, cornbread are square.” (Sorry about that.)

I always wondered how pi was actually calculated. One way is to measure the circumference and diameter of a circle and do the math, but that would be inaccurate by an amount equal to your measurement error. Some use the fraction 22/7 as a simple approximation, but that is not so accurate either. There does not appear to be one standard method. However, the most accurate ways are to use one of many infinite series such as Gregory-Leibniz or Nitakantha, to name a few, or use the arcsine method. Such series are fun only to mathematicians. For the rest of us, just press the pi button on your calculator. Using the pi button on the calculator in Microsoft Windows, I got 32 digits. That is usually enough.

How should you recognize Pi Day?  Eat some pie, use pi, or talk about the importance of pi to others, like your spouse. Better still, just think of pi as you indulge in an adult beverage at the end of the day. Oh, by the way. March 14 is also Einstein’s birthday. Another good reason to celebrate. Enjoy!