acos, acosf, acosl − arc cosine function

#include <math.h>

double acos(double x);
float acosf(float x);
long double acosl(long double x);

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.

SVID 3, POSIX, BSD 4.3, ISO 9899. The float and long double variants are C99 requirements.

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