#include <cstdio>

#include <algorithm>

#include <cstring>

using namespace std;

const double esp = 1e-;

const double PI = 3.14159265359;

int T,N,F,radii[];

int main()

{

    scanf("%d",&T);

    while(T--)

    {

        scanf("%d%d",&N,&F);

        F++;

        double low = ,high=,mid;

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

        {

            scanf("%d",&radii[i]);

            high = max(high,radii[i]*radii[i]*PI);

        }

        while(high-low>esp)

        {

            int piece = ;

            mid = (low+high)/;

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

            {

                double v = radii[i]*radii[i]*PI;

                int cnt = ;

                while((cnt+)*mid < v) cnt++;

                piece += cnt;

            }

            //printf("low=%f high=%f piece=%d\n",low,high,piece);

            if(piece >= F) low = mid;

            else high = mid;

        }

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

    }

}