acos, acosf—arc cosineSynopsis
#include <math.h> double acos(double x); float acosf(float x);
Description
acos computes the inverse cosine (arc cosine) of the input value.
Arguments to acos must be in the range -1 to 1.
acosf is identical to acos, except that it performs
its calculations on floats.
Returns
acos and acosf return values in radians, in the range of 0 to pi.
If x is not between -1 and 1, the returned value is NaN
(not a number), and the global variable errno is set to EDOM.