# Constant

## Definition

A literal number that represents a quantity all the time is called a constant.

The true meaning of the word constant is unchangeable. In algebra, a symbol, called literal number is used to represent an unchangeable quantity and it represents the same quantity all the time. Hence, the literal is called a constant.

### Examples

There are numerous examples for the constants in the universe. Some constant quantities are represented by some special symbols all over the world but the remaining constant quantities can be represented by any literal but the standard constant symbols should not be used to represent every unchangeable quantity.

#### Hours of a Day

John Napier introduced natural logarithmic system by considering an irrational number $2.71828182845904523536028747135266249775724709369995…$ as its base.

It is too difficult to remember and not easy to write it everywhere. So, he represented this irrational number by a letter $e$ and it is universally accepted.

$e = 2.71828182845904523536028747135266249775724709369995…$

Just write the symbol $e$ everywhere instead of writing this long number. So, the symbol e is basically called as a constant but it was introduced by the John Neper. Therefore, the constant $e$ is usually called as Napier constant.

$0.000001$ is one of the most famous small decimals.

A Greek symbol micro $(\mu)$ was introduced to represent millionth.

$$\mu = 0.000001 = 10^{-6} = \frac{1}{1000000}$$

The symbol $\mu$ represents this unique quantity. So, it is an example to a constant.

The value of the ratio of circumference to diameter of a circle is $3.1415926535897932384626433832795…$

It is an irrational number and constant even though the diameter of the circle is changed. A Greek symbol pi $(\pi)$ is used to denote this quantity.

$\pi = 3.1415926535897932384626433832795…$

The symbol $\pi$ is called as constant.