OAP/lab03/task9.cs

int[] x = new int[4];
        int[] y = new int[4];
        for (int i = 0; i < 4; ++i)
        {
            Console.Write("Введите (x" + i.ToString() + ",y" + i.ToString() + "): ");
            x[i] = Console.Read();
            y[i] = Console.Read();
            Console.ReadLine();
        }

        int a = (x[1] - x[0]) * (y[2] - y[1]) - (x[2] - x[1]) * (y[1] - y[0]);
        int b = (x[2] - x[0]) * (y[3] - y[2]) - (x[3] - x[2]) * (y[2] - y[0]);
        int c = (x[3] - x[0]) * (y[1] - y[3]) - (x[1] - x[3]) * (y[3] - y[0]);

        if ((a >= 0 && b >= 0 && c >= 0) || (a <= 0 && b <= 0 && c <= 0))
        {
            Console.WriteLine("Принадлежит треугольнику");
        }
        else
        {
            Console.WriteLine("Не принадлежит треугольнике");
        }
Console.ReadKey();