Trailing Zeroes

#include <stdio.h>
#include <math.h>
int main()
{
     int n;
     double a,b;
     scanf("%d", &n);
     while(n--)
     {
          scanf("%lf %lf", &a,&b);
          printf("%.4lf\n",pow((b*a)/(b+a),2));
     }
     return 0;
}

          printf("%.4g\n",pow((b*a)/(b+a),2));

$ ./a.out 
4
1 1
0.25
2 2
1
3 3
2.25
4 4
4