double
     acosh(double x);

     long double
     acoshl(long double x);

     float
     acoshf(float x);

DESCRIPTION

     The acosh() function computes the principle value of the inverse hyper-
     bolic cosine of x.  The result is in the range [0, +infinity].

SPECIAL VALUES

     acosh(1) returns +0.

     acosh(x) returns a NAN and raises the "invalid" floating-point exception
     for x < 1.

     acosh(+infinity) returns +infinity.

SEE ALSO

     asinh(3), atanh(3), exp(3), math(3)

STANDARDS

     The acosh() function conforms to ISO/IEC 9899:1999(E).

HISTORY

     The acosh() and acoshf() function appeared in 4.3BSD.

4.3 Berkeley Distribution      November 15, 2002     4.3 Berkeley Distribution