#include <time.h>
double cos(double x);
float cosf(float x);
cos() computes the principal value of the cosine of x. Express x in radians.
The cosine cos(x)
acos() and acosf(),
asin() and asinf(),
atan() and atanf(),
atan2() and atan2f(),
sin() and sinf(), and
tan() and tanf()