Уточнение корня уравнения методом Ньютона

Private Sub Command1_Click()
 
Dim X(200) As Single, Y(200) As Single
Dim a As Single
Dim b As Single, xx As Single, x1 As Single
Dim h As Single, xn As Single, xk As Single
Dim n As Integer
Dim i As Integer
a = InputBox("Введите начало участка")
b = InputBox("Vvedite B")
n = InputBox("Vvedite N")
h = (b - a) / (n - 1)
Label2.Caption = "Интервал от :" + Str(a) +" до "+ Str(b) + " Кол-во узлов=" + Str(n) + " h=" + Str(h)
 
For i = 1 To n
 X(i) = a + h * (i - 1)
 Y(i) = Sin(X(i)) + 0.3 * (X(i)) - 3.4
 List1.AddItem ("x(" + Str(i) + ")=" + Str(X(i)) + " y(" + Str(i) + ")=" + Str(Y(i)))
 Next i
e = 0.0001
  For i = 2 To n - 1
  If Y(i) * Y(i + 1) < 0 Then
   xn = X(i)
   xk = X(i + 1)
   xx = xn
333   X1 = xx
    xx = xk - (Sin(xk) + 0.3 * xk - 3.4 / Cos(xk))
     If (Sin(xx) + 0.3 * xx - 3.4) * (Sin(xk) + 0.3 * xk - 3.4) < 0 Then
      xn = xx
     Else
      xk = xx
     End If
     If Abs(X1 - xx) <= e Then
      nom = nom + 1
      List2.AddItem ("Корень касательной №" + Str(nom) + " xx=" + Str(xx) + " На участке=" + Str(i))
      Else
      GoTo 333
      End If
  End If
  Next i
End Sub