Построение графика квадратичной функции

Dim a As Single
Dim b As Single
Dim c As Single
Dim i As Integer
Dim y As Double
Dim x As Single
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
PictureBox1.Scale (-5, 8)-(5, -8)
a = TextBox1.Text
b = TextBox2.Text
c = TextBox3.Text
Picture1.Line (-5, 0)-(5, 0), vbBlue
For i = -5 To 5
y = x ^ 2 - 2 * x - 3
PictureBox1.PSet (i, 0), vbRed
PictureBox1.Print i
Next i
PictureBox1.Line (0, -8)-(0, 8), vbBlue
For i = -8 To 8
PictureBox1.PSet (0, i), vbRed
PictureBox1.Print i
Next i
For x = -5 To 5 Step 0.005
y = a * x * x + b * x + c
Picture1.PSet (x, y), vbRed
Next
End Sub
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button1.Click
Text1.Text = ""
Text2.Text = ""
Text3.Text = ""
PictureBox1.Cls
End Sub

    Dim Graph1 As Graphics
    Dim Pen1 As New Pen(Color.Black, 2)
    Dim Pen2 As New Pen(Color.Blue, 2)
    Dim DrawBrush As New SolidBrush(Color.Black)
    Dim DrawFont As New Font("Arial", 10)
    Dim X, Y As Single
    Dim Bitmap As New Bitmap(600, 600)

                  Graph1 = Graphics.FromImage(Bitmap)
        Graph1.Clear(Color.White)
  For Me.X = -300 To 300 Step 25
                Graph1.DrawString(X / 25, DrawFont, DrawBrush, X + 300, 300)
            Next X
            For Me.Y = -300 To 300 Step 25
                Graph1.DrawString(Y / 25, DrawFont, DrawBrush, 300, 300 - Y)
            Next Y
            Graph1.ScaleTransform(1, -1)
            Graph1.TranslateTransform(300, -300)
            Graph1.DrawLine(Pen1, -300, 0, 300, 0)
            Graph1.DrawLine(Pen1, 0, -300, 0, 300)
            For Me.X = -300 To 300 Step 25
                Graph1.DrawLine(Pen1, X, -5, X, 5)
            Next X
            For Me.Y = -300 To 300 Step 25
                Graph1.DrawLine(Pen1, -5, Y, 5, Y)
            Next Y
            For Me.X = -300 To 300 Step 0.005
                Y = A.Text * X ^ 2 + Bt.Text * X + Ct.Text
                Graph1.DrawEllipse(Pens.Red, X * 25, Y * 25, 1, 1)
            Next X