**acos**

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.
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
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