Why do they call it PI?
It was first called "pi" in 1706 by [the Welsh mathematician] William Jones, because pi is the first letter in the Greek word perimitros, which means "perimeter." It's a special number.
March 14, or 3/14, is known as “Pi Day” because of its resemblance to the first three digits in the decimal expansion of $pi$ (pi), which is defined as the ratio of a circle's circumference to its diameter: The true circle constant is the ratio of a circle's circumference to its radius, not to its diameter.
- Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant digits of π.
- Tau (constant) Edit. The Greek letter τ (tau) is a suggested symbol for the circle constant representing the ratio between circumference and radius. The constant is equal to 2π (2 times pi), and approximately 6.28.
- The Babylonians estimated pi to be about 25/8 (3.125), while the Egyptians estimated it to be about 256/81 (roughly 3.16). The Ancient Greek mathematician Archimedes of Syracuse (287-212 BC) is largely considered to be the first to calculate an accurate estimation of the value of pi.
Euler is the first person who started to use radian in trigonometry. The circumference of a unit circle is 2pi, therefore he defined 360 degrees be 2pi radian. A radian is the measure of an angle subtended at the centre of a circle by an arc equal in length to the radian.
- Radians measure angles by distance traveled. or angle in radians (theta) is arc length (s) divided by radius (r). A circle has 360 degrees or 2pi radians — going all the way around is 2 * pi * r / r. So a radian is about 360 /(2 * pi) or 57.3 degrees.
- Hence, anyone could use pi when they had a calculation involving half of tau." Tau, the 19th letter of the Greek alphabet, was chosen independently as the symbol for 2pi by Michael Hartl, physicist and mathematician and author of "The Tau Manifesto," and Peter Harremoës, a Danish information theorist.
- Every integer is a rational number, since each integer n can be written in the form n/1. For example 5 = 5/1 and thus 5 is a rational number. However, numbers like 1/2, 45454737/2424242, and -3/7 are also rational, since they are fractions whose numerator and denominator are integers.
Updated: 2nd October 2019