---
title: math.tanh
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/functions/math-trig/math-tanh
---

```
FLOAT math.tanh(FLOAT x)
```

**Available in:** all subroutines

Computes the hyperbolic tangent of its argument `x`.

## Parameters

`x` - Floating point value representing a hyperbolic angle.

## Return Value

Upon successful completion, this function returns the hyperbolic tangent of `x`.

If `x` is `math.NAN`, a NaN will be returned.

If `x` is ±0, `x` will be returned.

If `x` is `math.POS_INFINITY` or
`math.NEG_INFINITY`, ±1 will be returned.

If `x` is _subnormal_, a range error occurs and `x` will be returned.

## Errors

If the `x` argument is _subnormal_, then fastly.error
will be set to `ERANGE`.

## Example

```vcl
declare local var.fo FLOAT;

set var.fo = math.tanh(-1);
```