# ACOSH

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## NAME

acosh, acoshf,
acoshl − inverse hyperbolic cosine function

## SYNOPSIS

**#include
<math.h>**

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

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

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

Link with
*−lm*.

Feature Test
Macro Requirements for glibc (see
**feature_test_macros**(7)):

**acosh**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

**acoshf**(),
**acoshl**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

## DESCRIPTION

The
**acosh**() function calculates the inverse hyperbolic
cosine of *x*; that is the value whose hyperbolic
cosine is *x*.

## RETURN VALUE

On success,
these functions return the inverse hyperbolic cosine of
*x*.

If *x* is
a NaN, a NaN is returned.

If *x* is
+1, +0 is returned.

If *x* is
positive infinity, positive infinity is returned.

If *x* is
less than 1, a domain error occurs, and the functions return
a NaN.

## ERRORS

See
**math_error**(7) for information on how to determine
whether an error has occurred when calling these
functions.

The following
errors can occur:

Domain error: *x* is less than 1

*errno* is set to
**EDOM**. An invalid floating-point exception
(**FE_INVALID**) is raised.

## ATTRIBUTES

For an
explanation of the terms used in this section, see
**attributes**(7).

## CONFORMING TO

C99,
POSIX.1-2001. The variant returning *double* also
conforms to SVr4, 4.3BSD, C89.

## SEE ALSO

**asinh**(3),
**atanh**(3), **cacosh**(3), **cosh**(3),
**sinh**(3), **tanh**(3)

## COLOPHON

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