1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)acos.3 8.1 (Berkeley) 06/04/93 7.\" 8.Dd 9.Dt ACOS 3 10.Os 11.Sh NAME 12.Nm acos 13.Nd arc cosine function 14.Sh SYNOPSIS 15.Fd #include <math.h> 16.Ft double 17.Fn acos "double x" 18.Sh DESCRIPTION 19The 20.Fn acos 21function computes the principal value of the arc cosine of 22.Fa x . 23A domain error occurs for arguments not in the range [-1, +1]. 24For a discussion of error due to roundoff, see 25.Xr math 3 . 26.Sh RETURN VALUES 27The 28.Fn acos 29function returns the arc cosine in the range 30.Bq 0 , \*(Pi 31radians. 32On the 33.Tn VAX 34and 35.Tn Tahoe , 36if: 37.Bd -unfilled -offset indent 38.Pf \&| Ns Ar x Ns \&| > 1 , 39.Ed 40.Pp 41.Fn acos x 42sets the global variable 43.Va errno 44to 45.Dv EDOM 46and a reserved operand fault is generated. 47.Sh SEE ALSO 48.Xr sin 3 , 49.Xr cos 3 , 50.Xr tan 3 , 51.Xr asin 3 , 52.Xr atan 3 , 53.Xr atan2 3 , 54.Xr sinh 3 , 55.Xr cosh 3 , 56.Xr tanh 3 , 57.Xr math 3 , 58.Sh STANDARDS 59The 60.Fn acos 61function conforms to 62.St -ansiC . 63