#include<iostream>

#include<cmath>

#include<cstring>

#include<queue>

#include<vector>

#include<cstdio>

#include<algorithm>

#include<map>

#include<set>

#define rep(i,e) for(int i=0;i<(e);i++)

#define rep1(i,e) for(int i=1;i<=(e);i++)

#define repx(i,x,e) for(int i=(x);i<=(e);i++)

#define X first

#define Y second

#define PB push_back

#define MP make_pair

#define mset(var,val) memset(var,val,sizeof(var))

#define scd(a) scanf("%d",&a)

#define scdd(a,b) scanf("%d%d",&a,&b)

#define scddd(a,b,c) scanf("%d%d%d",&a,&b,&c)

#define pd(a) printf("%d\n",a)

#define scl(a) scanf("%lld",&a)

#define scll(a,b) scanf("%lld%lld",&a,&b)

#define sclll(a,b,c) scanf("%lld%lld%lld",&a,&b,&c)

#define IOS ios::sync_with_stdio(false);cin.tie(0)

#define lc idx<<1

#define rc idx<<1|1

#define rson mid+1,r,rc

#define lson l,mid,lc

using namespace std;

typedef long long ll;

template <class T>

void test(T a) {

    cout<<a<<endl;

}

template <class T,class T2>

void test(T a,T2 b) {

    cout<<a<<" "<<b<<endl;

}

template <class T,class T2,class T3>

void test(T a,T2 b,T3 c) {

    cout<<a<<" "<<b<<" "<<c<<endl;

}

const int inf = 0x3f3f3f3f;

const ll INF = 0x3f3f3f3f3f3f3f3fll;

const ll mod = 1e9+;

int T;

void testcase() {

    printf("Case %d: ",++T);

}

const int MAXN = 1e5+;

const int MAXM = ;

const double PI = acos(-1.0);

const double eps = 1e-;

double pie[MAXN];

int n,m;

int main() {

#ifdef LOCAL

    freopen("data.in","r",stdin);

#endif // LOCAL

    int T;

    scanf("%d",&T);

    while(T--) {

        scanf("%d%d",&n,&m);

        double maxx = ;

        for(int i=; i<n; i++) {

            scanf("%lf",&pie[i]);

            pie[i] *= pie[i];

            if(maxx<pie[i]) {

                maxx = pie[i];

            }

        }

        m  = m + ;

        double l = ;

        double r = maxx;

        double mid;

        while(r-l>eps) {

            mid = (r+l)/;

            int sum = ;

            for(int i=; i<n; i++) {

                if(pie[i]-mid>eps) {

                    sum += (int)pie[i]/mid;

                }

            }

            if(sum>=m) l = mid;

            else r = mid;

        }

        printf("%.4f\n",mid*PI);

    }

    return ;

}