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.\"     from: @(#)acosh.3	5.2 (Berkeley) 5/6/91
.\" $FreeBSD: src/lib/msun/man/acosh.3,v 1.11 2005/01/14 23:28:28 das Exp $
.\"
.Dd January 14, 2005
.Dt ACOSH 3
.Os
.Sh NAME
.Nm acosh ,
.Nm acoshf
.Nd inverse hyperbolic cosine functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In 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 .
If the argument is less than 1,
.Fn acosh
raises an invalid exception and returns an \*(Na.
.Sh SEE ALSO
.Xr asinh 3 ,
.Xr atanh 3 ,
.Xr exp 3 ,
.Xr fenv 3 ,
.Xr math 3
.Sh HISTORY
The
.Fn acosh
function appeared in
.Bx 4.3 .