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What is Pi Day and why do we care?

Rational thoughts about 3.14 on 3/14.

By Rich_Maloof Mar 14, 2013 4:33PM

Today’s date can be written as 3.14 — the same digits used to estimate π, the ratio of the circumference of a circle to its diameter.

In case you missed geometry class, pi is used in the formula πr2  to calculate the area of a circle: multiply pi (π) by the radius squared (r2). Back in the 1700s, a Swiss mathematician swiped π, the sixteenth letter of the Greek alphabet, from the first letter of periphereia, meaning periphery or circumference.

Photo: What is Pi Day / Jeffrey Coolidge/Getty ImagesBut pi is interesting as far as numbers go because even though a circle is a simple shape that every preschooler can recognize, the precise number represented by pi remains stubbornly elusive.

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What’s the last digit in pi? No one knows. It’s an irrational number, meaning that it can’t be properly expressed by any fraction or decimal. Pi continues infinitely without repeating. In 2010, a Japanese-American duo used a computer system to calculate pi to the five trillionth decimal place. You can see the first one million decimal places on this webpage (be patient — a million digits take a long time to load).

Some irrational numbers, being infinite and therefore literally beyond our comprehension, are referred to as transcendental numbers — lending the numerology of pi a nearly spiritual or religious quality. But for school teachers and math geeks across the land, Pi Day isn’t so much a high holiday as a teaching opportunity.

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Physicist Larry Shaw is credited with organizing the first Pi Day celebration at the San Francisco Exploratorium in 1988. A year later, the House of Representaives supported the designation of Pi Day. For the deeply geeky, Pi Approximation Day is observed on July 22 — since 22/7 approximates π in the form of a fraction.

Bing: More about Pi Day

Students across the country aren’t apt to get too excited about Pi Day since it’s not going to get them out of school anytime soon. But if they correctly calculate the area of a circle, a nice geometry teacher just might transect the diameter at a generous angle and slice them a nice sector of pie.

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Photo: What is Pi Day / Jeffrey Coolidge/Getty Images

Mar 14, 2013 6:14PM
A good day to rememger an old departed friend, Dr. Petr Beckmann, who wrote a wonderful book, "The History of Pi".    R.I.P. Petr.
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