March 14 is Pi Day - here's what that means
- March 14, written out as 3/14 in the US and a few other countries, is π day, as those are the first three digits of the famous number.
- π is one of the most important and fascinating numbers in math.
Happy π day!
March 14, when written out in the American date style of month/day, comes out as 3/14. That coincides with the three first digits of π: 3.14.π is one of the most important numbers in math. As you may recall from basic geometry, π is defined as the ratio of a circle's circumference to its diameter. So, anywhere where circles or cyclical things show up, π tends to show up as well. It would be impossible to do geometry, trigonometry, calculus, analysis of waves, or most branches of math without the concept of π.
As a number, π is also itself fascinating. π is an irrational number - it can't be written as a fraction of two integers, no matter what integers you choose. One consequence of that is that the infinite decimal expansion of π never adopts a repeating pattern.
π is actually a step further than an irrational number, and is what mathematicians call a transcendental number. There are plenty of irrational numbers - the square root of 2, or 3, or any prime number is irrational, as are cube roots and higher-power roots of primes. Transcendental numbers, like π, aren't the roots of any rational number. Another way of saying that is that π raised to any power is still irrational.
Even though circles, and therefore π, have been a subject of study for millennia - the great Greek mathematician Archimedes came up with a clever way of approximating π by drawing polygons inside and outside a circle to estimate the circle's circumference - π was only proven to be irrational in the 18th century, and transcendental in the 19th.
π day comes with a few caveats, the biggest being that most of the world doesn't write March 14 as 3/14, but instead as 14/3. Still, for residents of the countries that do, π day offers a fun chance to reflect on a very special number.