# Definition:Hyperbolic Cotangent/Real

## Definition

### Definition 1

The real hyperbolic cotangent function is defined on the real numbers as:

$\coth: \R_{\ne 0} \to \R$:
$\forall x \in \R_{\ne 0}: \coth x := \dfrac {e^x + e^{-x} } {e^x - e^{-x} }$

where it is noted that at $x = 0$:

$e^x - e^{-x} = 0$

and so $\coth x$ is not defined at that point.

### Definition 2

The real hyperbolic cotangent function is defined on the real numbers as:

$\coth: \R_{\ne 0} \to \R$:
$\forall x \in \R_{\ne 0}: \coth x := \dfrac {\cosh x} {\sinh x}$

where:

$\sinh$ is the real hyperbolic sine
$\cosh$ is the real hyperbolic cosine

It is noted that at $x = 0$ we have that $\sinh x = 0$, and so $\coth x$ is not defined at that point.

### Definition 3

The real hyperbolic cotangent function is defined on the real numbers as:

$\coth: \R_{\ne 0} \to \R$:
$\forall x \in \R_{\ne 0}: \coth x := \dfrac 1 {\tanh x}$

where $\tanh$ is the real hyperbolic tangent.

It is noted that at $x = 0$ we have that $\tanh x = 0$, and so $\coth x$ is not defined at that point.

## Also denoted as

The notation $\operatorname {cth} z$ can also be found for hyperbolic cotangent.

## Also see

• Results about the hyperbolic cotangent function can be found here.