#include <stdio.h>

 #include <math.h>

 const double eps = 1e-;

 double areas[];

 int main() {

     int case_n, n, f, m;

     double r, sum, l, mid, PI;

     int i;

     PI = acos(-);

     scanf("%d", &case_n);

     while (case_n--) {

         scanf("%d %d", &n, &f);

         sum = 0.0f;

         for (i=; i<n; ++i) {

             scanf("%lf", &r);

             areas[i] = PI*r*r;

             sum += areas[i];

         }

         l = 0.0f;

         ++f;

         r = sum/f;

         while (r-l > eps) {

             mid = (l+r)/;

             m = ;

             for (i=; i<n; ++i)

                 m += (int)(areas[i]/mid);

             if (m < f)

                 r = mid;

             else

                 l = mid;

         }

         printf("%.4lf\n", l);

     }

     return ;

 }