Реализация приближенного метода решения уравнения - Visual Basic .NET

Public Class Form3
    Private ww, hh As Integer
    Private xy() As PointF
    Private isLoad As Boolean
    Private pn0, pn2 As Pen
    Private Sub Form3_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        With PictureBox1
            ww = .Width / 2
            hh = .Height / 2
            .BorderStyle = BorderStyle.FixedSingle
            .BackColor = Color.White
        End With
        pn0 = New Pen(Brushes.Black, 1)
        pn2 = New Pen(Brushes.Red, 1)
    End Sub
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        isLoad = True
        Dim ff = Function(x) x ^ 6 - 2 * x ^ 5 + 3 * x - 8
        Dim stp As Double = 0.2
        ReDim xy(4 / stp)
        Dim i As Integer
        For xx = -2 To 2 Step stp
            xy(i) = New PointF(xx, ff(xx))
            i += 1
        Next
        PictureBox1.Invalidate()
    End Sub
    Private Sub PictureBox1_Paint(sender As System.Object, e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
        If Not isLoad Then Exit Sub
        Dim k As Integer = 20
        Dim g As Graphics = e.Graphics
        g.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias
        g.TranslateTransform(ww, hh)
        g.ScaleTransform(1, -1)
        'оси координат
        g.DrawLine(pn0, New Point(0, hh), New Point(0, -hh))
        g.DrawLine(pn0, New Point(-ww, 0), New Point(ww, 0))
        'отметки на осях
        Dim ax() As Point = {New Point(-2, 0), New Point(-1, 0), New Point(1, 0), New Point(2, 0)}
        Dim ay(19) As Point
        Dim t As Integer = 1
        For i = 0 To ay.Length / 2 - 1
            ay(i) = New Point(0, -t)
            ay(i + ay.Length / 2) = New Point(0, t)
            t += 1
        Next
        'масштабирование
        Dim mm As New Drawing2D.Matrix
        mm.Scale(k, k, Drawing2D.MatrixOrder.Append)
        mm.TransformPoints(xy)
        mm.TransformPoints(ax)
        mm.TransformPoints(ay)
        'отметки на осях
        Dim ss As Integer = 5
        For i = 0 To ax.Length - 1
            g.DrawLine(pn0, ax(i), New Point(ax(i).X, ax(i).Y + ss))
        Next
        For i = 0 To ay.Length - 1
            g.DrawLine(pn0, ay(i), New Point(ay(i).X + ss, ay(i).Y))
        Next
        'кривая
        g.DrawLines(pn2, xy)
    End Sub
End Class