 
			| GNU/Linux | CentOS 5.6 | |
|  | acos(3) |  | 
acos, acosf, acosl − arc cosine function
#include <math.h>
double
acos(double x); 
float acosf(float x); 
long double acosl(long double x);
Link with −lm.
The acos() function calculates the arc cosine of x; that is the value whose cosine is x. If x falls outside the range −1 to 1, acos() fails and errno is set.
The acos() function returns the arc cosine in radians and the value is mathematically defined to be between 0 and PI (inclusive).
| EDOM | x is out of range. | 
SVr4, POSIX.1-2001, 4.3BSD, C89. The float and long double variants are C99 requirements.
asin(3), atan(3), atan2(3), cacos(3), cos(3), sin(3), tan(3)
|  | acos(3) |  |