Circle of death

//Bismillahir Rahmanir Rahim
/******Harun Or Rashid******/
/***********Template Starts Here***********/
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<cctype>
#include<cstdlib>
#include<string>
#include<vector>
#include<set>
#include<stack>
#include<queue>
#include<map>
#include<algorithm>
using namespace std;

#define MEM(a,b) memset(a,b,sizeof(a))
#define CLR(a) memset(a,0,sizeof(a))
#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)>(b)?(b):(a))
#define ABS(a) ((a)>0? (a):(-(a)))
#define SQ(a) ((a)*(a))
#define SZ(a) (int)a.size()
#define FORN(i,n) for(i=1;i<=n;i++)
#define FORAB(i,a,b) for(i=a;i<=b;i++)
#define ALL(V) V.begin(),V.end()
#define pb(a) push_back(a)
#define pr(a) cout<<a<<endl
#define pf printf
#define sf scanf
#define swap(a,b) (a ^= b, b ^= a, a ^= b)
#define PI acos(-1)
#define x first
#define y second
#define eps 1e-6

typedef int D;
typedef long long int LLD;
typedef unsigned long long int LLU;
typedef vector<D> VI;
typedef set<D> SI;
typedef vector<D>::iterator Viti;

/***********Template Ends Here***********/

double det(int x1,int y1,int c1,int x2,int y2,int c2,int x3,int y3,int c3)
{
    double res=x1*(y2*c3-c2*y3)-y1*(c3*x2-c2*x3)+c1*(y3*x2-x3*y2);
    return res;
}

int main()
{
    int T,n,i,j,k,l,cnt,prob;
    double area,d1,d2,d3,d4,D;
    vector<pair<int,int> >V;
    cin>>T;
    while(T--)
    {
        cin>>n;
        pair<int,int>point;
        V.clear();
        for(i=0; i<n; i++)
        {
            cin>>point.x>>point.y;
            V.pb(point);
        }
        cnt=prob=0;
        for(i=0; i<n; i++)
        {
            for(j=i+1; j<n; j++)
            {
                for(k=j+1; k<n; k++)
                {
                    prob=prob+n-3;
                    area=det(V[i].x,V[i].y,1,V[j].x,V[j].y,1,V[k].x,V[k].y,1);
                    if(area)
                    {
                        for(l=0; l<n; l++)
                        {
                            if(l==i||l==j||l==k) continue;
                            d1=area*(V[l].x*V[l].x+V[l].y*V[l].y);
                            d2=V[l].x*det(V[i].x*V[i].x+V[i].y*V[i].y,V[i].y,1,V[j].x*V[j].x+V[j].y*V[j].y,V[j].y,1,V[k].x*V[k].x+V[k].y*V[k].y,V[k].y,1);
                            d3=V[l].y*det(V[i].x*V[i].x+V[i].y*V[i].y,V[i].x,1,V[j].x*V[j].x+V[j].y*V[j].y,V[j].x,1,V[k].x*V[k].x+V[k].y*V[k].y,V[k].x,1);
                            d4=det(V[i].x*V[i].x+V[i].y*V[i].y,V[i].x,V[i].y,V[j].x*V[j].x+V[j].y*V[j].y,V[j].x,V[j].y,V[k].x*V[k].x+V[k].y*V[k].y,V[k].x,V[k].y);
                            D=d1-d2+d3-d4;
                            if(area<0&&D>=0) cnt++;
                            if(area>0&&D<=0) cnt++;
                        }
                    }
                }
            }
        }
        printf("%.6lf\n",(double)cnt/prob+eps);
    }
    return 0;
}