NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## NAME

## SYNOPSIS

## DESCRIPTION

## RETURN VALUE

## ERRORS

## ATTRIBUTES

## CONFORMING TO

## SEE ALSO

## COLOPHON

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

acos, acosf, acosl − arc cosine function

**#include
<math.h>**

**double
acos(double** *x***);
float acosf(float**

long double acosl(long double

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*

These functions
calculate the arc cosine of *x*; that is the value
whose cosine is *x*.

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.

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.

For an
explanation of the terms used in this section, see
**attributes**(7).

C99, POSIX.1-2001, POSIX.1-2008.

The variant
returning *double* also conforms to SVr4, 4.3BSD,
C89.

**asin**(3),
**atan**(3), **atan2**(3), **cacos**(3),
**cos**(3), **sin**(3), **tan**(3)

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