#include <iostream>
#include <iomanip>
#include<queue>
#include<math.h>
#include<algorithm>
#include<string.h>
#include<stdlib.h>
#include<stdio.h>
#include<iomanip>
#include<string.h>
#include<sstream>
#include<string>
#include<queue>
#define MAX 5842
//¶¨Ò庯Êý¶Î
#define repf(i,a,b) for(int i =(a);i<(b);i++)
#define repfe(i,a,b) for(int i =(a);i<=(b);i++)
using namespace std;
double r[10010];
#define PI acos(-1.0)
int n,f;
bool cmp(int a,int b )
{
    return a>b ;
}
int num(double a)
{
    long long sum = 0 ;
    for(int i = 0 ; i < n ; i++)
    {
        sum +=(int)(r[i]/a);

    }
    if(sum>=f)
        return 1 ;
    else{
        return 0 ;
    }
}
int main() {
    int t;
     scanf("%d", &t);
    while (t--){
        scanf("%d%d", &n, &f);
        f++;
        for (int i = 0; i < n; i++){
        scanf("%lf", &r[i]);
        r[i]=r[i]*r[i]*PI;
        }
        sort(r,r+n,cmp);
        double high = r[0],low = 0 , mid ;
        while(high-low>0.00001)
        {
            mid=(high+low)/2;
             if (num(mid))low = mid;
             else {
                high = mid;
             }

        }
         mid = (high + low) / 2;
           printf("%.4f\n", mid);
    }
    return 0 ;
}