NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## NAME

## SYNOPSIS

## DESCRIPTION

## RETURN VALUE

## ERRORS

## ATTRIBUTES

## CONFORMING TO

## SEE ALSO

## COLOPHON

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

acosh, acoshf, acoshl − inverse hyperbolic cosine function

**#include
<math.h>**

**double
acosh(double** *x***);
float acoshf(float**

long double acoshl(long double

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*

These functions
calculate the inverse hyperbolic cosine of *x*; that is
the value whose hyperbolic cosine is *x*.

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.

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.

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

C99, POSIX.1-2001, POSIX.1-2008.

The variant
returning *double* also conforms to SVr4, 4.3BSD,
C89.

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

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part of release 4.04 of the Linux *man-pages* project.
A description of the project, information about reporting
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http://www.kernel.org/doc/man−pages/.

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