# e constant

e constant or Euler's number is a mathematical constant. The e constant is real and irrational number.

e = 2.718281828459...

## Definition of e

The e constant is defined as the limit:

#### Alternative definitions

The e constant is defined as the limit:

The e constant is defined as the infinite series:

## Properties of e

#### Reciprocal of e

The reciprocal of e is the limit:

#### Derivatives of e

The derivative of the exponential function is the exponential function:

(e x)' = ex

The derivative of the natural logarithm function is the reciprocal function:

(loge x)' = (ln x)' = 1/x

#### Integrals of e

The indefinite integral of the exponential function ex is the exponential function ex.

ex dx = ex+c

The indefinite integral of the natural logarithm function loge x is:

∫ loge x dx = ∫ ln x dx = x ln x - x +c

The definite integral from 1 to e of the reciprocal function 1/x is 1:

### Base e logarithm

The natural logarithm of a number x is defined as the base e logarithm of x:

ln x = loge x

### Exponential function

The exponential function is defined as:

f (x) = exp(x) = ex

### Euler's formula

The complex number e has the identity:

e = cos(θ) + i sin(θ)

i is the imaginary unit (the square root of -1).

θ is any real number.