# ACOS

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## 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**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

## DESCRIPTION

The
**acos**() function calculates 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
**attributes**(7).

## CONFORMING TO

C99,
POSIX.1-2001. 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 3.53 of the Linux *man-pages* project.
A description of the project, and information about
reporting bugs, can be found at
http://www.kernel.org/doc/man−pages/.