.\" Copyright (c) 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" from: @(#)acos.3 5.1 (Berkeley) 5/2/91
.\" %FreeBSD: src/lib/msun/man/acos.3,v 1.6.2.2 2001/03/06 16:46:24 ru Exp %
.\"
.\" $FreeBSD$
.Dd May 2, 1991
.Dt ACOS 3
.Os
.Sh 名称
.Nm acos ,
.Nm acosf
.Nd 逆余弦関数
.Sh 書式
.Fd #include <math.h>
.Ft double
.Fn acos "double x"
.Ft float
.Fn acosf "float x"
.Sh 解説
.Fn acos
および
.Fn acosf
関数は、
.Fa x
の逆余弦の主値を計算します。
[-1, +1] の区間外の引数によって、領域エラーが発生します。
丸めによる誤差の議論は、
.Xr math 3
を参照してください。
.Sh 戻り値
.Fn acos
および
.Fn acosf
関数は、
.Bq 0 , \*(Pi
ラジアンの区間の逆余弦を返します。
.Tn VAX
および
.Tn Tahoe
では、
.Bd -unfilled -offset indent
.Pf \&| Ns Ar x Ns \&| > 1
.Ed
.Pp
の場合に、
.Fn acos x
はグローバル変数
.Va errno
を
.Er EDOM
に設定し、予約されたオペランドフォルトが生成されます。
.Sh 関連項目
.Xr asin 3 ,
.Xr atan 3 ,
.Xr atan2 3 ,
.Xr cos 3 ,
.Xr cosh 3 ,
.Xr math 3 ,
.Xr sin 3 ,
.Xr sinh 3 ,
.Xr tan 3 ,
.Xr tanh 3
.Sh 規格
.Fn acos
関数は、
.St -isoC
に適合しています。
