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

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

4. 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

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

9. 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 2005. • 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.