// 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;}