.\" Copyright (c) 1991 Regents of the University of California.
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.\"     from: @(#)acosh.3	5.2 (Berkeley) 5/6/91
.\"	$Id: acosh.3,v 1.1.1.1 1994/08/19 09:39:41 jkh Exp $
.\"
.Dd May 6, 1991
.Dt ACOSH 3
.Os BSD 4.3
.Sh NAME
.Nm acosh ,
.Nm acoshf
.Nd inverse hyperbolic cosine functions
.Sh SYNOPSIS
.Fd #include <math.h>
.Ft double
.Fn acosh "double x"
.Ft float
.Fn acoshf "float x"
.Sh DESCRIPTION
The
.Fn acosh
and the 
.Fn acoshf
functions compute 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
and the 
.Fn acoshf
functions
return 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 .