The letter π The constant is named "π" because it is the first letter of the Greek words: περιφέρεια = periphery περιφέρεια = periphery περίμετρος = perimeter περίμετρος = perimeter

Definition In Euclidean plane geometry, π is defined as the ratio of a circle's circumference to its diameter. π = c/d = c/2r

Calculating π π can be empirically measured by drawing a large circle, then measuring its diameter and circumference, since the circumference of a circle is always π times its diameter. π can also be calculated using purely mathematical methods

Principle of Archimedes' method to approximate π n=5 n=6 n=8

ninscribed polygondescribed polygon 32, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Infinit e ππ

a few excitements... In 2002 Kanada and fellow researchers at Japan's Information Technology Center set a new record for finding the number of digits of π 1.24 trillion decimal places. This calculation took about 602 hours. Chao Lu of China recited π on 67,890 decimal places on 20 November Rose Hare is the youngest person to make the Pi World Ranking List (age: 3 years 356 days) Math lovers celebrate March 14 (or "3-14") as Pi Day. The theory of elliptic curves and complex multiplication derives the approximation which is valid to about 30 digits.