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.\"     from: @(#)acos.3	5.1 (Berkeley) 5/2/91
.\" $FreeBSD: src/lib/msun/man/acos.3,v 1.13 2005/01/14 23:28:28 das Exp $
.\"
.Dd January 14, 2005
.Dt ACOS 3
.Os
.Sh NAME
.Nm acos ,
.Nm acosf
.Nd arc cosine functions
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In math.h
.Ft double
.Fn acos "double x"
.Ft float
.Fn acosf "float x"
.Sh DESCRIPTION
The
.Fn acos
and the
.Fn acosf
functions compute the principal value of the arc cosine of
.Fa x .
A domain error occurs for arguments not in the range
.Bq -1 , +1 .
For a discussion of error due to roundoff, see
.Xr math 3 .
.Sh RETURN VALUES
The
.Fn acos
and the
.Fn acosf
functions return the arc cosine in the range
.Bq 0 , \*(Pi
radians.
If:
.Bd -unfilled -offset indent
.Pf \&| Ns Ar x Ns \&| > 1 ,
.Ed
.Pp
.Fn acos x
raises an invalid exception and returns an \*(Na.
.Sh SEE ALSO
.Xr asin 3 ,
.Xr atan 3 ,
.Xr atan2 3 ,
.Xr cos 3 ,
.Xr cosh 3 ,
.Xr fenv 3 ,
.Xr math 3 ,
.Xr sin 3 ,
.Xr sinh 3 ,
.Xr tan 3 ,
.Xr tanh 3
.Sh STANDARDS
The
.Fn acos
function conforms to
.St -isoC .