public static TAMGIAC NhapTamGiac()
        {
            TAMGIAC tg;

            Console.WriteLine("Nhap dinh A:");
            tg.A = XL_DIEM.NhapDiem();
            Console.WriteLine("Nhap dinh B:");
            tg.B = XL_DIEM.NhapDiem();
            Console.WriteLine("Nhap dinh C:");
            tg.C = XL_DIEM.NhapDiem();

            return(tg);
        }
        public static DAGIAC NhapDaGiac()
        {
            DAGIAC dg;

            Console.WriteLine("Nhap so dinh cua da giac");
            int N = int.Parse(Console.ReadLine());

            dg.dsDinh = new DIEM[N];
            for (int i = 0; i < N; i++)
            {
                Console.WriteLine($"Nhap dinh {i + 1}:");
                dg.dsDinh[i] = XL_DIEM.NhapDiem();
            }

            return(dg);
        }