[求助]在picturebox控件上画函数图像
如题，在picturebox1控件上画函数图像（比如y=x^2+3*x），单击button1时，开始画图像.单击button2时，picturebox1上的图像清除。
十分感谢各位给与解答。
程序代码：Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim myPen As Graphics = PictureBox1.CreateGraphics
Dim x1 As Single, y1 As Single, x As Single, y As Single, r As Single, width As Single, height As Single
r = 1
For x1 = 1 To 20
y1 = 6 * x1 - 3
width = r * 20
height = r * 20
x = x1 - width / 1
y = y1 - height / 1000
myPen.FillEllipse(Brushes.Red, x, y, width, height)
Next
'上面是一个例子，自己琢磨如何绘图吧
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
PictureBox1.Image = Nothing '清除已绘制或加载的图像
End Sub
End Class
