public static int FoundN(AreaType areaType, double tolerantion)
        {
            int n = 1;
            double integral = 0;

            while (n <= MAX_N)
            {
                if (areaType == AreaType.Rectangle)
                    integral = RectangleMethod(X1, X2, n);

                if (areaType == AreaType.Trapezoid)
                    integral = TrapezoidMethod(X1, X2, n);

                double difference = Math.Abs(INTEGRAL_VALUE - integral);
                double differenceInPercent = (difference / Result.INTEGRAL_VALUE) * 100.0;
                if (differenceInPercent <= tolerantion)
                {
                    break;
                }

                n++;
            }
            return n;
        }
        private static double DegreeToRadian(double angle)
        {
            return Math.PI * angle / 180.0;
        }

        private static double Function(double x)
        {
            return Math.Cos(DegreeToRadian(x));
        }


//button
tolerantion = Convert.ToDouble(numericUpDown2.Value);

            textBox1.Text = Convert.ToString(Result.FoundN(AreaType.Rectangle, tolerantion));
            textBox2.Text = Convert.ToString(Result.FoundN(AreaType.Trapezoid, tolerantion));