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# acosh

## man page of acosh

### acosh: inverse hyperbolic cosine function

```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);

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.

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

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

COLOPHON
This  page  is  part of release 3.27 of the Linux man-pages project.  A
description of the project, and information about reporting  bugs,  can
be found at //www.kernel.org/doc/man-pages/.

2010-09-20                          ACOSH(3)
```