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 ||
       _ISOC99_SOURCE; or cc -std=c99
       acoshf(), acoshl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
       || _ISOC99_SOURCE; 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.

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

COLOPHON
       This page is part of release 3.23 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can