using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication8
{
    class Program
    {
        static void Main()
        {
            double Fx = 0, fx = 0, X_prev = 0, epsilone_requested = 0.02D, epsilone = 0, X = 0.5D;

            do
            {
                X_prev = X;
                Fx =  Math.Cos(X) - Math.Pow(X, 3);
                fx = -Math.Sin(X) - 3 * Math.Pow(X, 2);
                X -= Fx / fx;
                epsilone = Math.Abs(X - X_prev);
                Console.WriteLine("X = {0}\nEpsilone = {1}\n", X, epsilone);
            }
            while (epsilone > epsilone_requested);
            Console.ReadKey();

        }
    }
}