#include<bits/stdc++.h>
using  namespace std;
int main ()
{
    int t,cs=1,ox,oy,ax,ay,bx,by;
    double oa,ob,ab,o;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d %d %d %d %d %d",&ox,&oy,&ax,&ay,&bx,&by);
        oa=((ax-ox)*(ax-ox))+((ay-oy)*(ay-oy));
        oa=sqrt(oa);
        ob=((bx-ox)*(bx-ox))+((by-oy)*(by-oy));
        ob=sqrt(ob);
        ab= ((bx-ax)*(bx-ax))+((by-ay)*(by-ay));
        ab= sqrt(ab);
        o=acos(((oa*oa)+(ob*ob)-(ab*ab)));
        cout<<"o angle is -- "<<o<<endl;


    }

    return 0;
}