cos, cosf, cosl - cosine function

Syntax	#include <math.h> double cos(double x); C11 float cosf(float x); long double cosl(long double x); (End)
Description	These functions compute the cosine of the floating-point number x, which specifies an angle in radians.
Return val.	cos(x)	The return value is a floating-point number in the range [-1.0, +1.0].
See also	acos(), asin(), atan(), atan2(), sin(), tan(), math.h.