程序代码：

#include <stdio.h>
#include <math.h>

int main()
{
    double a, b, c, h1, h2, k1, k2, l1, l2;
    double cosine;
    
    printf("input arguments by this order:\n"
           "    a, b, c, h1, h2, k1, k2, l1, l2\n");
    if (scanf("%lf, %lf, %lf, %lf, %lf, %lf, %lf, %lf, %lf",
              &a, &b, &c, &h1, &h2, &k1, &k2, &l1, &l2) != 9)
    { puts("inputs invalid!"); return 1; }
    
    a *= a; b *= b; c *= c;
    cosine = (h1*h2/a + k1*k2/b + l1*l2/c)
            / sqrt( (h1*h1/a + k1*k1/b + l1*l1/c)
                   * (h2*h2/a + k2*k2/b + l2*l2/c) );
    printf("cosine = %lf\n", cosine);
    
    return 0;
}