$ ./cos-2
cos(2)=-0.416147
cos(2gradusa)=0.999391
$ cat cos-2.c
#include <stdio.h>
#include <math.h>

void main() {
        printf("cos(2)=%f\n",cos(2));
        printf("cos(2gradusa)=%f\n",cos(2*M_PI/180));
}