#include <bits/stdc++.h>
using namespace std;
#define MAX 1000003
#define tiny 0.000000001
#define pi acos(-1)
int N,F;
int r[MAX];
bool check(double x){
	double np=0;//number of person
	for(int i=1;i<=N;i++){
		np+= double (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*10,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<<fixed<<setprecision(6)<<pi*upper<<endl;
	}
}