static void DemoDiemToaDo()
        {
            DiemToaDo a = XL_Diem.NhapDiem();
            DiemToaDo b = XL_Diem.NhapDiem();

            Console.WriteLine($"Khoang cach 2 diem la {XL_Diem.TinhKhoangCach2Diem(a, b)}");
        }
        public static double TinhChuViDaGiac(DaGiac daGiac)
        {
            double ChuVi = 0;

            if (daGiac.ToaDoCacDinh.Length < 3)
            {
                Console.WriteLine("Da giac khong hop le");
                return(ChuVi);
            }
            for (int i = 0; i < daGiac.ToaDoCacDinh.Length - 1; i++)
            {
                ChuVi += XL_Diem.TinhKhoangCach2Diem(daGiac.ToaDoCacDinh[i], daGiac.ToaDoCacDinh[i + 1]);
            }
            ChuVi += XL_Diem.TinhKhoangCach2Diem(daGiac.ToaDoCacDinh[0], daGiac.ToaDoCacDinh[daGiac.ToaDoCacDinh.Length - 1]);
            return(ChuVi);
        }