NAME

     acosh - inverse hyperbolic cosine function

SYNOPSIS

     #include <math.h>

     double acosh(double x);

DESCRIPTION

     The  acosh()  function  calculates  the  inverse  hyperbolic
     cosine of x; that is the value whose hyperbolic cosine is x.
     If x is less than 1.0, acosh()  returns  not-a-number  (NaN)
     and errno is set.

ERRORS

     EDOM x is out of range.

CONFORMING TO

     SVID 3, POSIX, BSD 4.3, ISO 9899

SEE ALSO

     asinh(3), atanh(3), cosh(3),