---
name: "acosh"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/acosh"
---

# acosh(3)

inverse hyperbolic cosine functions

## NAME

**acosh**, **acoshf**, **acoshl** – inverse hyperbolic cosine functions

## LIBRARY

Math Library (libm, -lm)

## SYNOPSIS

**#include \<math.h\>**

*double*\

**acosh**(*double x*);

*float*\

**acoshf**(*float x*);

*long* *double*\

**acoshl**(*long double x*);

## DESCRIPTION

The **acosh**(), **acoshf**(), and **acoshl**() functions compute the inverse hyperbolic cosine of the real argument *x*. For a discussion of error due to roundoff, see [math(3)](/math/3.md).

## RETURN VALUES

These functions return the inverse hyperbolic cosine of *x*. If the argument is less than 1, **acosh**() raises an invalid exception and returns an .

## SEE ALSO

[asinh(3)](/asinh/3.md), [atanh(3)](/atanh/3.md), [exp(3)](/exp/3.md), [fenv(3)](/fenv/3.md), [math(3)](/math/3.md)

## HISTORY

The **acosh**(), **acoshf**(), and **acoshl**() functions appeared in 4.3BSD, FreeBSD 2.0, and FreeBSD 10.0, respectively.