# Constants

Mathematical constants are symbols that represent useful numbers.

The circle constant τ (tau) is a number approximately equal to 6.283. The number is defined as the length of a circle's circumference divided by the length of its radius.

The greek letter π (pi) is a naturally occurring number that is defined by any circle's circumference divided by its diameter.

Euler's number is a naturally occurring number related to exponential growth and exponential decay.

The golden ratio is a number represented by the greek letter ϕ (phi). The value of ϕ is approximately 1.618 and is a naturally occurring number in nature. The golden ratio is often associated with the golden rectangle whose sides form a ratio equal to ϕ.

The letter "i" is used in mathematics to represent the square root of negative one. The letter is also used to denote the complex part of a complex number.