lightoj - 1433 - Minimum Arc Distance

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
    int t;
    cin>>t;
    for(int i=1;i<=t;i++)
    {
        double ox,oy,ax,ay,bx,by,O,A,B,ang;
        cin>>ox>>oy>>ax>>ay>>bx>>by;
        O=sqrt((bx-ax)*(bx-ax)+(by-ay)*(by-ay));
        A=sqrt((ox-bx)*(ox-bx)+(oy-by)*(oy-by));
        B=sqrt((ox-ax)*(ox-ax)+(oy-ay)*(oy-ay));
        ang=acos(((A*A)+(B*B)-(O*O)) / (2.0*A*B));
        ang*=A;
        cout<< "Case "<<i<< ": "<<setprecision(8)<<fixed<<ang<<endl;
    }
}