// poj3122

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstring>

#include<cstdio>

#include<cmath>

#define LL long long

#define inf 2147483640

#define Pi acos(-1.0)

#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);

using namespace std;

int n,f,r[1000010];

double a[1000010];

bool ok(double m) {

    int sum=0;

    for (int i=1;i<=n;i++) sum+=floor(a[i]/m);

    return sum>=f+1;

}

int main() {

    int T;

    scanf("%d",&T);

    while (T--) {

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

        double maxl=-1;

        for (int i=1;i<=n;i++) {

            scanf("%d",&r[i]),a[i]=r[i]*r[i]*Pi;

            maxl=max(maxl,a[i]);

        }

        double l=0.0,r=maxl;

        while (r-l>1e-5) {

            double mid=(l+r)/2;

            if (ok(mid)) l=mid;

            else r=mid;

        }

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

    }

    return 0;

}