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. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" from: @(#)acos.3 5.1 (Berkeley) 5/2/91 29.\" 30.Dd July 31, 2008 31.Dt ACOS 3 32.Os 33.Sh NAME 34.Nm acos , 35.Nm acosf , 36.Nm acosl 37.Nd arc cosine functions 38.Sh LIBRARY 39.Lb libm 40.Sh SYNOPSIS 41.In math.h 42.Ft double 43.Fn acos "double x" 44.Ft float 45.Fn acosf "float x" 46.Ft long double 47.Fn acosl "long double x" 48.Sh DESCRIPTION 49The 50.Fn acos , 51.Fn acosf , 52and 53.Fn acosl 54functions compute the principal value of the arc cosine of 55.Fa x . 56.Sh RETURN VALUES 57These functions return the arc cosine in the range 58.Bq 0 , \*(Pi 59radians. 60If: 61.Bd -unfilled -offset indent 62.Pf \&| Ns Fa x Ns \&| > 1 , 63.Ed 64.Pp 65.Fn acos x 66raises an invalid exception and returns an \*(Na. 67.Sh SEE ALSO 68.Xr asin 3 , 69.Xr atan 3 , 70.Xr atan2 3 , 71.Xr cos 3 , 72.Xr cosh 3 , 73.Xr fenv 3 , 74.Xr math 3 , 75.Xr sin 3 , 76.Xr sinh 3 , 77.Xr tan 3 , 78.Xr tanh 3 79.Sh STANDARDS 80The 81.Fn acos , 82.Fn acosf , 83and 84.Fn acosl 85functions conform to 86.St -isoC-99 . 87