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Good Question: What Is Pi?

MINNEAPOLIS (WCCO) -- On Pi Day, Sartell teacher Jennifer Kiewel wore her Pi Earrings and Pi Day Tattoos. Lindsey Smith's made a pie with the symbol for Pi branded into the crust.

And Michael Porter recited 145 digits of Pi: "3.14159265."

When a tornado wiped out his North Minneapolis kitchen, he and his wife Marie had a backsplash epiphany. They'd design it tiling digits of pi.

Marie blogged her instructions and in one month got 11,000 hits.

Each black tile represents a digit, so the first column has 3 black tiles, with 7 white tiles above it. The second column has 1 black tile with 8 white tiles above it.

"We're starting in the corner with 3.14 and it carries around the kitchen," said Porter.

On March 14, people celebrate 3.14 as Pi Day. The U.S. House declared it Pi Day in 2008. But what is pi and why is it such a big deal?

"This is one of our holiest days. We're celebrating here at school," said Brian Ribnick, a math teacher at Metcalf Junior High in Burnsville.

When he started there years ago, he was assigned to room 314. He promptly put a decimal point between the 3 and the 14.

"Pi is a number first approximated in the second century BC by Archimedes," said Ribnick. Archimedes was obsessed with circles and realized that, if you take the circumference of a circle and divide it by the diameter, you always get the same number.

"If you divide those two numbers its always right smack around 3. No matter how small or big the circle is," he said.

In 1761, a Swiss mathematician, Johann Heinrich Lambert, made another discovery.

"This number is an irrational number, which means it never ends, it never repeats, you can't really write it down," said Ribnick.

That's why pi is represented as the Greek letter. The number cannot fully be expressed. The formula for pi is circumference divided by diameter.

So what's it used for, besides calculating measurements of circles?

"Pi is used in engineering, astronomy, all fields of mathematics," said Ribnick. "It's not too easy to put a tape measure through the diameter of the Earth, but you could measure the outside, then using pi you could determine the diameter of the earth."

It's also used to determine your hat size. Measure the circumference of your head, divide that by Pi, and you'll get the diameter of your head, which is your hat size.

"It's used in finding volumes in spheres, surface areas of spheres," said Ribnick. "It's one of the 5 most important numbers in all of math."

Porter agrees.

"Circles are everywhere. In math, it keeps popping up, and some of us love it."

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