If you've ever taken any kind of math class, you will have heard about pi... you just may not remember exactly what it is or what it's used for. You know that it is equal to around 3.14 (with a bunch of other numbers on the end that never repeat themselves), but you may not know that pi is "the ratio of the circumference of a circle to its diameter." There are other things you may not know about this mysterious number either, like just how old it really is. Here is the history behind pi that you may never have heard before.

## Pi in ancient times

The concept of pi has been around for about 4,000 years. Although the numbers following the decimal point were slightly different back then, pi was being used for calculations beginning with the ancient Babylonians. They calculated the area of a circle by multiplying the square of its radius by three, meaning that pi was equal to around 3 or, to be more precise, 3.125.

An artifact called the Rhind Papyrus that dates back to around 1650 B.C. (just slightly more recent than the Babylonian artifacts dealing with pi) shows that the Egyptians found that pi was equal to around 3.1605, a slightly different number. It was found in much the same way, however, which led to it being used in other civilizations as well.

## Archimedes

The very first official calculation of pi was carried out by one of the greatest mathematicians in world history, Archimedes, who lived between 287 and 212 B.C. Instead of just using circles, he used the Pythagorean Theorem to find the area of a polygon inscribed within a circle and the area of a polygon that was formed around the circle. The idea behind this was that the circle lay between these two polygons, and the areas of the two polygons gave the "upper and lower bounds for the area of the circle." His experiments proved that pi, although imprecise, was equal to something between 3 1/7 and 3 10/71.

## Pi in other cultures

After Archimedes' groundbreaking discovery, several other mathematicians all over the world attempted to extend the number of decimal places that come after the 3 in pi. Chinese, Arab, and Indian mathematicians all used difficult, time-consuming methods to try to expand the number instead of using the path Archimedes had already laid out for them. This led to more versions of pi, all of which had different numbers after the decimal point.

## Pi in its current form

Finally, in the 17th century, pi began to become a more solid, stable value - although it will always be an approximation. Sir Isaac Newton used what he called a "binomial theorem" to calculate 16 decimal places in pi. A few centuries later, a mathematician from India named Svinivasa Ramanujan developed a method of calculating pi that could be incorporated into algorithms for the computer. Around a century after that, in the 2000s, computers were able to calculate the value of pi to an incredible 31,415,926,535,897 decimal places, making it much more accurate than ever before.

## What is pi used for now?

The current version of pi to 39 decimal places is: 3.141592653589793238462643383279502884197, a number often memorized by math and science lovers. Pi is used in many math problems that deal with the length of curves, arcs, circular areas, ellipses, and volumes. It is used in both engineering and physics as well to calculate the motion of things, such as the vibration patterns of strings, electrical currents, and the swinging arc of a pendulum.