#include <bits/stdc++.h>
using namespace std;
#define MAX 1000003
#define tiny 0.00000001
#define pi 3.14
int N,F;
int r[MAX];
void merge(int arr[], int l, int m, int r) 
{ 
	int i, j, k; 
	int n1 = m - l + 1; 
	int n2 = r - m; 

	int L[n1], R[n2]; 
	
	for (i = 0; i < n1; i++) 
		L[i] = arr[l + i]; 
	for (j = 0; j < n2; j++) 
		R[j] = arr[m + 1+ j]; 
	i = 0; 
	j = 0; 
	k = l;
	while (i < n1 && j < n2) 
	{ 
		if (L[i] >= R[j]) 
		{ 
			arr[k] = L[i]; 
			i++; 
		} 
		else
		{ 
			arr[k] = R[j]; 
			j++; 
		} 
		k++; 
	} 

	while (i < n1) 
	{ 
		arr[k] = L[i]; 
		i++; 
		k++; 
	} 

	while (j < n2) 
	{ 
		arr[k] = R[j]; 
		j++; 
		k++; 
	} 
} 

void mergeSort(int arr[], int l, int r) 
{ 
	if (l < r) 
	{ 
		int m = l+(r-l)/2; 

		mergeSort(arr, l, m); 
		mergeSort(arr, m+1, r); 

		merge(arr, l, m, r); 
	} 
} 
bool check(double x){
	int np=0;//number of person
	for(int i=1;i<=N;i++){
		np+= int (pi*r[i]*r[i]/x);
	}
	if(np >= F+1) return true;
	else return false;
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	int n;
	cin>>n;
	double upper=MAX,lower=tiny;
	double x;
	while(n--){
		cin>>N>>F;
		for(int i=1;i<=N;i++) cin>>r[i];
		mergeSort(r,1,N);
		while(upper - lower > tiny){
			x=double((upper+lower)/2);
			if(check(x)) lower=x;
			else upper=x;
		}
		cout<<setprecision(7)<<fixed<<x<<endl;
	}
}