.\" Copyright (c) 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" %sccs.include.redist.man%
.\"
.\"     @(#)acos.3	5.1 (Berkeley) 05/02/91
.\"
.Dd 
.Dt ACOS 3
.Os
.Sh NAME
.Nm acos
.Nd arc cosine function
.Sh SYNOPSIS
.Fd #include <math.h>
.Ft double
.Fn acos "double x"
.Sh DESCRIPTION
The
.Fn acos
function computes the principal value of the arc cosine of
.Fa x .
A domain error occurs for arguments not in the range [-1, +1].
For a discussion of error due to roundoff, see
.Xr math 3 .
.Sh RETURN VALUES
The 
.Fn acos
function returns the arc cosine in the range
.Bq 0 , \*(Pi
radians.
On the
.Tn VAX
and
.Tn Tahoe ,
if:
.Bd -unfilled -offset indent
.Pf \&| Ns Ar x Ns \&| > 1 ,
.Ed
.Pp
.Fn acos x
sets the global variable
.Va errno
to
.Dv EDOM
and a reserved operand fault is generated.
.Sh SEE ALSO
.Xr sin 3 ,
.Xr cos 3 ,
.Xr tan 3 ,
.Xr asin 3 ,
.Xr atan 3 ,
.Xr atan2 3 ,
.Xr sinh 3 ,
.Xr cosh 3 ,
.Xr tanh 3 ,
.Xr math 3 ,
.Sh STANDARDS
The
.Fn acos
function conforms to
.St -ansiC .