#include <math.h>
float cosf(float x);
cosf returns the radian circular cosine of x.
If |x| > 10^9, errno is set to EDOM and cosf returns HUGE_VALF.
If x is NaN, cosf returns x.
If |x| is ?, cosf returns NaN with invalid signal .
cosf conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).