From Bwtm

This page is about Mathematics.


Fibonacci Numbers

Golden ratio

φ (pronounced “phi”) 1.61803398875…

Equal to about 1.61803398875…, the irrational number φ is also known as the golden ratio or divine proportion. It is essential to geometry, and can be expressed as the ratio of a regular pentagon’s diagonal to the length of a side. Two numbers (say, a and b) are considered in the golden ratio if (a+b)/b = φ.

e (pronounced “ee”)

Equal to about 2.71828182846..., e was discovered by Jacob Bernoulli, who first discovered it in a formula for calculating compound interest.

√2 (pronounced “root two”)

Last and most venerable is the square root of 2 (written √2), which is equal to about 1.41421356237…Sometimes known as the Pythagorean constant, √2 is also the length of the hypotenuse of a right triangle, whose other sides both have length 1.


Today is Mar. 14, or “Pi Day” (really, π Day) when mathletes and numberphiles celebrate the mathematical constant π, which is equal to 3.141592653…It’s a particularly special Pi Day because the year is 2015, bringing today’s date (3.14.15) two digits closer to π’s infinite decimal expansion. Part of π’s charm is its mix of measurable and undiscoverable: we know that π is exactly the ratio of a circle’s circumference to its diameter, and yet it is infinitely unknowable—the sequence of numbers following the decimal point in π has no pattern and goes on forever.


The other irrational numbers we could celebrate instead of pi