public static string XuatDiem(DIEM a) { return($"({a.X},{a.Y})"); }
public static double TinhKhoangCach(DIEM a, DIEM b) { return(Math.Sqrt((a.X - b.X) * (a.X - b.X) + (a.Y - b.Y) * (a.Y - b.Y))); }