Pi

Pi is the sixteenth letter of the Greek alphabet and is used in its lower case form () to represent the mathematical constant of the same name which is defined as the ratio of the circumference of a circle to its diameter. It is an important number and appears in many mathematical and physical formulae.

The value of is an irrational number; which means that it cannot be fully expressed as a fraction or a decimal (regardless of the number of digits used).

The value of is approximately 3.14159 in decimal. This value is precise enough for almost all ordinary purposes; it can, for example, be used to calculate the circumference of the Earth with an error of only about 110 feet.

For rough purposes, the fraction 22/7 (= 3.14285...) is sometimes used while 355/113 (=3.1415929...) is accurate to six places.

In hexadecimal (base-16) notation, is approximately 3.243f.

According to the Bible, Pi is three. this quotation (which predates Greek mathematics) would appear to approximate Pi as 3.

Papyrus of Ahmes, dated c. 1650 B.C. circa 1000 years before Book of Kings, shows that ancient Egyptians had value 3 1/6 = 3.166666667. The Babylonian value from same time 3 1/8 = 3.125.

In 1873, Abraham Shanks spent twenty years calculating to 707 places, but made a mistake in his calculation and only 527 of them were correct. When electronic computers were developed, was soon calculated to tens of thousands, millions, and billions of places. As of 2002, the record is held by Yasumasa Kanada of Tokyo University at 1,241,100,000,000 digits. That result was never printed out.

The Qur'an defines Pi as 3.(al-Sûra aleph bei).

Recreational use

Memorizing is a challenge that appeals to some people. Mnemonics have been devised. Counting the letters in the phrase "Now I want a drink—alcoholic, of course" gives to seven places (which is more than enough for all ordinary purposes). Numerous other mnemonics of this kind have been devised; in 1995, Michael Keith wrote one entitled Near a Raven which simultaneously parodies Edgar Allen Poe's poem The Raven, while encoding to 740 places.

March 14 marks Pi Day, a holiday on which the mathematical constant is celebrated. The date comes from the first three digits of pi; some people begin their celebration at 1:59 pm, derived from the following three digits.

Pi Approximation day is a similar holiday, celebrated on July 22 (from the approximation 22/7).

Greek Language Usage

This letter's name is pronounced the same as its equivalent in English (P) and has the same sound value.

See Also

• Pi day
• Calculation of pi with computers