en.wikipedia.org/wiki/Pi

The number π is a mathematical constant, the ratio of a circle's circumference to its diameter, ... The symbol used by mathematicians to represent the ratio of a circle's circumference to its diameter is the lowercase Greek letter π, sometimes ...

www.angio.net/pi/whypi.html

Pi (π) is the ratio of the circumference of a circle to its diameter. ... Archimedes used this trick with 96 sided polygons to correctly estimate Pi to about two digits ...

www.livescience.com/29197-what-is-pi.html

Apr 30, 2013 ... Pi (π), the 16th letter of the Greek alphabet, is used to represent the most widely known mathematical constant. By definition, pi is the ratio of the ...

mathforum.org/dr.math/faq/faq.pi.html

What is Pi? Who first used Pi? How do you find it? What is it for? How many digits is it?

www.newyorker.com/tech/elements/pi-day-why-pi-matters

Mar 13, 2015 ... They're calling this the Pi Day of the century: 3.14.15. ... memorized these and similar formulas for the S.A.T.s and then never again used them, ...

www.reference.com/math/pi-used-5fba050fbb78ef3d

Pi is used to find the circumference and area of a circle. It is also used to find the volume and surface area of a sphere, cone and cylinder. Pi has applications ...

www.mathsisfun.com/numbers/pi.html

Then the circumference (all the way around the circle) is Pi. pi circle diameter ... There are many special methods used to calculate π and here is one you can try ...

www.scientificamerican.com/article/what-is-pi-and-how-did-it

According to Petr Beckmann's A History of Pi, the Greek letter was first used for this purpose by William Jones in 1706, probably as an abbreviation of periphery, ...

www.piday.org/learn-about-pi

Pi is a constant number, meaning that for all circles of any size, Pi will be the same. ... The mathematician Archimedes used polygons with many sides to ...

www.dkfindout.com/us/math/numbers/pi

Pi is a useful number that is used in mathematical formulas. It is also written as the π symbol. The number pi is usually written as 3.14. This has been rounded to ...