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.\" $Id: acos.3,v 1.4 1993/10/29 22:57:17 jtc Exp $ 34.\" 35.Dd May 2, 1991 36.Dt ACOS 3 37.Os 38.Sh NAME 39.Nm acos 40.Nd arc cosine function 41.Sh SYNOPSIS 42.Fd #include <math.h> 43.Ft double 44.Fn acos "double x" 45.Sh DESCRIPTION 46The 47.Fn acos 48function computes the principal value of the arc cosine of 49.Fa x . 50A domain error occurs for arguments not in the range [-1, +1]. 51For a discussion of error due to roundoff, see 52.Xr math 3 . 53.Sh RETURN VALUES 54The 55.Fn acos 56function returns the arc cosine in the range 57.Bq 0 , \*(Pi 58radians. 59On the 60.Tn VAX 61and 62.Tn Tahoe , 63if: 64.Bd -unfilled -offset indent 65.Pf \&| Ns Ar x Ns \&| > 1 , 66.Ed 67.Pp 68.Fn acos x 69sets the global variable 70.Va errno 71to 72.Dv EDOM 73and a reserved operand fault is generated. 74.Sh SEE ALSO 75.Xr sin 3 , 76.Xr cos 3 , 77.Xr tan 3 , 78.Xr asin 3 , 79.Xr atan 3 , 80.Xr atan2 3 , 81.Xr sinh 3 , 82.Xr cosh 3 , 83.Xr tanh 3 , 84.Xr math 3 85.Sh STANDARDS 86The 87.Fn acos 88function conforms to 89.St -ansiC . 90