OpenDarwin 7.2.1 - man page for acosh (opendarwin section 3)

ACOSH(3)			   BSD Library Functions Manual 			 ACOSH(3)

NAME
     acosh -- inverse hyperbolic cosine function

SYNOPSIS
     #include <math.h>

     double
     acosh(double x);

DESCRIPTION
     The acosh() function computes the inverse hyperbolic cosine of the real argument x.

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), infnan(3), math(3), matherr(3)

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

HISTORY
     The acosh() function appeared in 4.3BSD.

4.3 Berkeley Distribution		November 15, 2002		4.3 Berkeley Distribution