/*
  [NWERC'06] Pie
  by: Jan Kuipers
*/

using namespace std;

#include <cstdio>
#include <cmath>
#include <vector>

const int rmax = 10000;

int main () {

  int runs;
  scanf ("%i",&runs);

  while (runs--) {
    int N,F;
    scanf ("%i %i",&N,&F);
    vector<int> r(N);
    for (int i=0; i<N; i++) scanf ("%i",&r[i]);

    double lo=0, hi=M_PI*rmax*rmax;
    for (int go=0; go<100; go++) {
      double x = (lo+hi)/2;
      int cnt=0;
      for (int i=0; i<N; i++) cnt += (int)floor(M_PI*r[i]*r[i]/x);
      if (cnt<F+1) hi=x; else lo=x;
    }

    printf ("%.3f\n",lo);
  }

  return 0;
}