public static void Main(string[] args)

        {

            Triangle1 t = new Triangle1(6,8, 9);

            Console.WriteLine("Perimeter {0}, Face{1},.", t.Perimeter(), t.Face());

        }

        interface ITriangle

        {

            double Perimeter();

            double Face();

        }

    class Triangle1

    {

        private double a, b, c;

        public Triangle1(double a, double b, double c)

        {

            this.a = a;

            this.b = b;

            this.c = c;

        }

        public double Perimeter()

        {

            return a + b + c;

        }

        public double Face()

        {

            double p = this.Perimeter() / 2;

            return Math.Sqrt(p * (p - a) * (p - b) * (p - c));

        }

    }

​