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

```
FLOAT math.acosh(FLOAT x)
```

**Available in:** all subroutines

Computes the inverse hyperbolic cosine of its argument `x`.

## Parameters

`x` - Floating point value representing the area of a hyperbolic sector.

## Return Value

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

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

If `x` is +1, +0 will be returned.

If `x` is `math.POS_INFINITY`,
`math.POS_INFINITY` will be returned.

If `x` is `math.NEG_INFINITY`,
a domain error occurs and a NaN will be returned.

For finite values of `x` < 1, a domain error occurs and a NaN will be returned.

## Errors

If the `x` argument is finite and less than +1.0, or is
`math.NEG_INFINITY`,
then `fastly.error` will be set to `EDOM`.

## Example

```vcl
declare local var.fo FLOAT;

set var.fo = math.acosh(10);
```