Problem Link : http://www.lightoj.com/volume_showproblem.php?problem=1433

#include <bits/stdc++.h>

#define pii pair <int,int>
#define sc scanf
#define pf printf
#define Pi 2*acos(0.0)
#define ms(a,b) memset(a, b, sizeof(a))
#define pb(a) push_back(a)
#define MP make_pair
#define oo 1<<29
#define dd double
#define ll long long
#define EPS 10E-10
#define ff first
#define ss second
#define MAX 10000
#define CIN ios_base::sync_with_stdio(0)
#define SZ(a) (int)a.size()
#define getint(a) scanf("%d",&a)
#define getint2(a,b) scanf("%d%d",&a,&b)
#define getint3(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define loop(i,n) for(int i=0;i<n;i++)
#define TEST_CASE(t) for(int z=1;z<=t;z++)
#define PRINT_CASE printf("Case %d: ",z)
#define all(a) a.begin(),a.end()
#define intlim 2147483648
#define inf 1000000
#define rtintlim 46340
#define llim 9223372036854775808
#define rtllim 3037000499
#define ull unsigned long long
#define I int

using namespace std;

/* Bits operation */
int Set(int n,int pos)  { return n = n | 1<<pos;}
bool check(int n,int pos) { return n & 1<<pos;}
int Reset(int n, int pos) { return n=n & ~(1<<pos);}

int main()
{
    ///freopen("in.txt","r",stdin);
    ///freopen("out.txt","w",stdout);
    int t,x,y;
    getint(t);

    TEST_CASE(t)
    {
        getint2(x,y);
        pii o(x,y);
        getint2(x,y);
        pii a(x,y);
        getint2(x,y);
        pii b(x,y);
        double ab=sqrt((a.ff-b.ff)*(a.ff-b.ff)+(a.ss-b.ss)*(a.ss-b.ss));
        double oa=sqrt((a.ff-o.ff)*(a.ff-o.ff)+(a.ss-o.ss)*(a.ss-o.ss));
        double ob=sqrt((b.ff-o.ff)*(b.ff-o.ff)+(b.ss-o.ss)*(b.ss-o.ss));
        double angle=acos(((oa*oa)+(ob*ob)-(ab*ab))/(2*oa*ob));
        PRINT_CASE;
        pf("%lf\n",angle*ob);
    }
    return 0;
}