1.\" Copyright (c) 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)acos.3 5.1 (Berkeley) 5/2/91 33.\" $FreeBSD: src/lib/msun/man/acos.3,v 1.13 2005/01/14 23:28:28 das Exp $ 34.\" 35.Dd January 14, 2005 36.Dt ACOS 3 37.Os 38.Sh NAME 39.Nm acos , 40.Nm acosf 41.Nd arc cosine functions 42.Sh LIBRARY 43.Lb libm 44.Sh SYNOPSIS 45.In math.h 46.Ft double 47.Fn acos "double x" 48.Ft float 49.Fn acosf "float x" 50.Sh DESCRIPTION 51The 52.Fn acos 53and the 54.Fn acosf 55functions compute the principal value of the arc cosine of 56.Fa x . 57A domain error occurs for arguments not in the range 58.Bq -1 , +1 . 59For a discussion of error due to roundoff, see 60.Xr math 3 . 61.Sh RETURN VALUES 62The 63.Fn acos 64and the 65.Fn acosf 66functions return the arc cosine in the range 67.Bq 0 , \*(Pi 68radians. 69If: 70.Bd -unfilled -offset indent 71.Pf \&| Ns Ar x Ns \&| > 1 , 72.Ed 73.Pp 74.Fn acos x 75raises an invalid exception and returns an \*(Na. 76.Sh SEE ALSO 77.Xr asin 3 , 78.Xr atan 3 , 79.Xr atan2 3 , 80.Xr cos 3 , 81.Xr cosh 3 , 82.Xr fenv 3 , 83.Xr math 3 , 84.Xr sin 3 , 85.Xr sinh 3 , 86.Xr tan 3 , 87.Xr tanh 3 88.Sh STANDARDS 89The 90.Fn acos 91function conforms to 92.St -isoC . 93