**acos**

**ACOS(3)** Linux Programmer's Manual **ACOS(3)**
NAME
acos, acosf, acosl - arc cosine function
SYNOPSIS
#include <math.h>
double acos(double x);
float acosf(float x);
long double acosl(long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see **feature_test_macros(7)**):
acosf(), acosl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
These functions calculate the arc cosine of x; that is the value whose
cosine is x.
RETURN VALUE
On success, these functions return the arc cosine of x in radians; the
return value is in the range [0, pi].
If x is a NaN, a NaN is returned.
If x is +1, +0 is returned.
If x is positive infinity or negative infinity, a domain error occurs,
and a NaN is returned.
If x is outside the range [-1, 1], a domain error occurs, and a NaN is
returned.
ERRORS
See **math_error(7)** for information on how to determine whether an error
has occurred when calling these functions.
The following errors can occur:
Domain error: x is outside the range [-1, 1]
errno is set to EDOM. An invalid floating-point exception
(FE_INVALID) is raised.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
**tributes(7)**.
+-------------------------+---------------+---------+
|Interface | Attribute | Value |
+-------------------------+---------------+---------+
|acos(), acosf(), acosl() | Thread safety | MT-Safe |
+-------------------------+---------------+---------+
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
SEE ALSO
**asin(3)**, **atan(3)**, **atan2(3)**, **cacos(3)**, **cos(3)**, **sin(3)**, **tan(3)**
COLOPHON
This page is part of release 5.05 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 **ACOS(3)**

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