Returns the hyperbolic arc cosine of its argument.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <math.h>

      double acosh  (double x);

      float acoshf  (float x);

      long double acoshl  (long double x);

1  –  Argument

 x

    A radian expressed as a real value in the domain [1, +Infinity].

2  –  Description

    The acosh functions return the hyperbolic arc cosine of x for x
    in the domain [1, +Infinity], where acosh(x) = ln(x + sqrt(x**2 -
    1)).

    The acosh function is the inverse function of cosh where
    acosh(cosh(x)) = |x|.

    x < 1 is an invalid argument.