Se considera punctele A,B,C,D varfuri ale unui patrulater convex. Ce conditii indeplineste ABCD daca vectorii de pozitie ai varfurilor verifica relatia [tex] r^{-\ \textgreater \ } _{A} +5r^{-\ \textgreater \ } _{C} =r^{-\ \textgreater \ } _{B} +5r^{-\ \textgreater \ } _{D} ?[/tex] Multumesc mult!