//1969
#include <cstdio>
#include <string>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
const int NFMAX = 10000 +10;
const double EPS = 1e-6;
const double PI = acos(-1.0);
int n,f;
double v[NFMAX];
bool check(double pie) {
	int i,s = 0;
	for (i=0;i<n;i++) s += v[i] / pie;
	return (s >= f+1);
}
int main() {
	int i,j,cas;
	double dl,dr,dmid;
	scanf("%d",&cas);
	while (cas --) {
		scanf("%d %d",&n,&f);
		dl = dr = 0;
		for (i=0;i<n;i++) {
			double r;
			scanf("%lf",&r);
			v[i] = r*r*PI;
			dr = max(dr,v[i]);
		}
		while (dr-dl >= EPS) {
			dmid = (dr+dl) / 2.0;
			if (check(dmid)) dl = dmid;
			else dr = dmid;
		}
		printf("%.4lf\n",dr);
	}
}