#include<cstdio>

 #include<cmath>

 #define pi acos(-1.0)

 #define eps 0.000001

 #define maxn 10009

 using namespace std;

 double area[maxn];

 int main()

 {

     int t,n,f,ri;

     double r=-;

     scanf("%d",&t);

     while(t--)

     {

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

         f=f+;

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

         {

             scanf("%d",&ri);

             area[i]=ri*ri*pi;

             if(area[i]>r)r=area[i];

         }

         double l=0.0;

         while(r-l>eps)

         {

             double mid=(r+l)/;

             int cnt=;

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

                 cnt+=floor(area[i]/mid);

             if(cnt>=f)l=mid;

             else r=mid;

         }

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

     }

     return ;

 }