.\" Copyright (c) 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" %sccs.include.redist.roff%
.\"
.\"     @(#)acosh.3	8.1 (Berkeley) 06/04/93
.\"
.Dd 
.Dt ACOSH 3
.Os BSD 4.3
.Sh NAME
.Nm acosh
.Nd inverse hyperbolic cosine function
.Sh SYNOPSIS
.Fd #include <math.h>
.Ft double
.Fn acosh "double x"
.Sh DESCRIPTION
The
.Fn acosh
function computes the inverse hyperbolic cosine
of the real
argument
.Ar x .
For a discussion of error due to roundoff, see
.Xr math 3 .
.Sh RETURN VALUES
The
.Fn acosh
function
returns the inverse hyperbolic cosine of
.Ar x .
On the
.Tn VAX
and
.Tn Tahoe ,
if the argument is less than one
.Fn acosh
sets the global variable
.Va errno
to
.Er EDOM
and
causes a reserved operand fault.
.Sh SEE ALSO
.Xr asinh 3 ,
.Xr atanh 3 ,
.Xr exp 3 ,
.Xr infnan 3
.Xr math 3 ,
.Sh HISTORY
The
.Fn acosh
function appeared in 
.Bx 4.3 .