График(найдите ошибку)!! - VB

Формулировка задачи:

Picture1.Line (5, 160)-(420, 160)
  Picture1.Line (210, 50)-(210, 260)
   
  Picture1.Line (420, 160)-(410, 155)
  Picture1.Line (420, 160)-(410, 165)
   
  Picture1.Line (210, 50)-(205, 60)
  Picture1.Line (210, 50)-(215, 60)
  
  Picture1.Line (207 - 3, 246)-(212 + 4, 246)
  Picture1.Line (207 - 3, 66)-(212 + 4, 66)
   
  For i = 1 To 10
    Picture1.Line (210 + Round(i * 19), 160 - 3)-(210 + Round(i * 19), 160 + 3)
    Picture1.Line (210 - Round(i * 19), 160 - 3)-(210 - Round(i * 19), 160 + 3)
  Next
   
  For i = 0 To 210
  X = i / 19 - 10
    'X2 = (i + 3) / 19 - 10
    'Y1 = 32
    Y = X * X * X + X * X + 3
    Picture1.Line (Round(i) + 21, 156 - Y)-(Round(i + 1) + 21, 156 - Y)
  Next

Решение задачи: «График(найдите ошибку)!!»

textual
                            Листинг программы 
                        

                            Private Sub Command1_Click()
X1 = -20: X2 = 20: Y1 = 1000: Y2 = -1000
Picture1.Scale (X1, Y1)-(X2, Y2)
Picture1.Line (X1, 0)-(X2, 0)
  Picture1.Line (0, Y1)-(0, Y2)
   
  Picture1.Line (X2, 0)-(X2 - 1, -30)
  Picture1.Line (X2, 0)-(X2 - 1, 30)
   
  Picture1.Line (0, Y1)-(-1, Y1 - 40)
  Picture1.Line (0, Y1)-(1, Y1 - 40)
  
  Picture1.Line (-1, Y1 / 2)-(1, Y1 / 2)
  Picture1.Line (-1, Y2 / 2)-(1, Y2 / 2)
   
  For i = X1 To X2 Step 4
    Picture1.Line (i, -20)-(i, 20)
  Next
   
  For x = X1 To X2 Step 0.01
  
    'X2 = (i + 3) / 19 - 10
    'Y1 = 32
    Y = x * x * x '+ x * x + 3
    Picture1.PSet (x, Y), vbRed '-(x, Y)
  Next
End Sub
                        