#include <iostream>
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <cmath>
#define pi acos(-1.0)
using namespace std;
const int maxn = 10005;
int r[maxn];
double v[maxn];
int n,f;
bool check(double x)
{
int cnt = 0;
int t = lower_bound(v,v + n,x) - v;
for(int i = t; i < n; i ++)
cnt += (int)(v[i] / x);
if(cnt >= f+1)
return true;
else
return false;
}
int main()
{
int t;
cin>>t;
while(t--)
{
cin>>n>>f;
for(int i = 0; i < n; i ++)
{
cin>>r[i];
v[i]= pi * r[i] * r[i] * 1;
}
if(n == 1)
printf("%.4lf
",v[0] / (f + 1));
else
{
sort(v,v + n);
double l = 0.0,r = v[n-1];
while(l + 1e-4 < r)
{
double mid = (l + r) / 2;
if(check(mid))
l = mid;
else
r = mid;
}
printf("%.4lf
",l);
}
}
return 0;
}