#include<stdio.h>

 #include<string.h>

 #include<iostream>

 #include<algorithm>

 #include<math.h>

 const double eps=1e-;

 const double pi=acos(-);

 using namespace std;

 int N,F;

 int V[];

 bool test(double  x){

 int ans=;

 for(int i=;i<N;i++){

     ans+=int(V[i]/x);

 }

 if(ans>=(F+))

     return true;

 else return false;

 }

 int main(){

 int t;

 cin>>t;

 while(t--){

     cin>>N>>F;

     double max=0.0;

     double low=0.0;

     double mid;

     for(int i=;i<N;i++){

         cin>>V[i];

         V[i]*=V[i];

         if(V[i]>max)

             max=V[i];

     }

     while(low+1e-<max){

         mid=(max+low)/;

         if(test(mid)==true)low=mid;

         else max=mid;

     }

     mid*=acos(-);

     printf("%.4f\n",mid);

 }return ;

 }