The Thursday Ten: Ten interesting facts about pi

This is post number 100. The square root of 100, as it so happens, is ten. Appropriate, I’d say.

So, the subject of this week’s Thursday Ten is π, or pi. I had intended on doing this post on ten mathematical constants, but pi turned out to have so much fun stuff about it, I decided to do the whole post on it. You remember the formulae for the area and circumference of a circle, right?

Area = πr2, where r is the radius;

Circumference = 2πr, or πd, where d is the diameter.

Diagram showing the diameter, radius, chord, tangent and secant of a circle (source: Wikimedia Commons; used under the GNU Free Documentation License)

Ten Interesting Facts About pi:

  1. Pi is also known as Archimedes’ constant. Through the use of polygons that circumscribed and inscribed in a circle, he estimated that the value of pi was between 3 17 and 3 1071.
  2. Pi is irrational, meaning that it cannot be expressed in the form ab, where a and b are integers and b is not equal to zero. It’s also a transcendental number, meaning that it isn’t algebraic (i.e. the root of a non-constant polynomial equation with rational coefficients).
  3. Pi has been calculated to as many as ten trillion digits, and no repeating pattern has been found. You can see the first million digits here. Using more than a few digits is hardly worth it; estimating the circumference of the earth using a nine-digit value of pi comes within a quarter of an inch, and estimating the circumference of the known universe using a 39-digit approximation gets you within the diameter of a hydrogen atom. And, as Piper Bayard reminds us, we managed to get to the moon using slide rules, on which the rough estimate of pi is shown.
  4. The value of pi was used as a secret code in Alfred Hitchcock’s Torn Curtain and the Sandra Bullock movie The Net.
  5. March 14 (3.14) is Pi Day. It’s celebrated at 1:59 PM. Albert Einstein’s birthday, as it so happens, is celebrated on March 14.
  6. Al-Khwarizmi, who lived in Babylon about 800 AD, estimated the value of pi as 3.1416 (the value most of us learned to use in the pre-calculator days). The word “algorithm” is based on his name.
  7. Pi shows up in the formula for calculating the probability density function for the normal curve.
  8. In 1897, the State of Indiana fixed the value of pi at 3.2. And there are those that argue that pi=4.
  9. The use of pi to denote the ratio between the circumference of a circle and its diameter is only about 300 years old. William Jones introduced it in 1706, and Leonhard Euler popularized it.
  10. It’s a known fact that the circumference of a jack o’lantern divided by its diameter gives us pumpkin pi…

My thanks to Wikipedia and Random Facts for their assistance. Hope you’ve enjoyed it…

6 thoughts on “The Thursday Ten: Ten interesting facts about pi

  1. You say that this post got the most hits for you so far. One possible reason is that you posted this right before the movie “Life of Pi” was released and the topic was prominent in the public eye up until Oscar time and has probably remained of interest since then. That’s one theory that seems pretty good to me.

    Tossing It Out


  2. I am impressed that you were able to hold off from posting this on 3/14. Or something. This is one of those totally math-ishy posts that my son would love. He’s 13. I just smile and try to pretend I understand. Nice to meet you.

    FYI: I only type with 6 fingers! I keep thinking: if I’m really going to be a writer, I should learn how to type properly! 😉


    1. The only reason I didn’t post it in 3/14 was that I wasn’t aware that there was an official day for it. I also missed Star Wars day (May the Fourth).


    1. Thanks. Most of the things I found out about it had to do with people memorizing the digits, and that really didn’t seem all that interesting. As I said, using more and more digits doesn’t get you any closer to the answer. For 99.9% of calculations, 3.1416 is as far as you really need to go. The joke, on the other hand, really appealed to me. Glad you liked it.


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