如何用vb的方法编出一元二次的图像

Option Explicit

Private Sub Form_Click()
Dim i, a, b, c

On Error GoTo EEE
a = InputBox("a")
b = InputBox("b")
c = InputBox("c")
Picture1.Cls
Picture1.Scale (-Picture1.Width / 30, Picture1.Height / 30)-(Picture1.Width / 30, -Picture1.Height / 30)
Picture1.Line (-Picture1.Width / 30, 0)-(Picture1.Width / 30, 0)
Picture1.Line (0, Picture1.Height / 30)-(0, -Picture1.Height / 30)
For i = -Picture1.Width / 30 To Picture1.Width / 30
Picture1.Line (i, a * i * i + b * i + c)-(i + 1, a * (i + 1) * (i + 1) + b * (i + 1) + c)
Next i
EEE:
End Sub

什么是一元二次的图像