Построение графика функции - VB (61235)

Формулировка задачи:

ошибку выдает. как исправить?

Option Explicit
Dim x, y, t, a As Double
Dim i As Integer
Private Sub Command1_Click()
a = Val(Text1.Text)
Picture1.Scale (-6, 10)-(6, -5)
Picture1.Line (-10, 0)-(5, 0), vbBlue
For i = -5 To 6
Picture1.PSet (i, 0)
Picture1.Print i
Next i
Picture1.Line (0, 10)-(0, -10), vbBlue
For i = -1 To 6
Picture1.PSet (0, i)
Picture1.Print i
Next i
 
For t = -6 To 6 Step 0.001
If t = -1 Then t = -0.9
x = (3 * a * t) / (1 + t ^ 3)
y = (3 * a * t ^ 2) / (1 + t ^ 3)
Picture1.PSet (x, y)
Next t
End Sub

Решение задачи: «Построение графика функции»

textual
                            Листинг программы 
                        

                            Dim x#, y#, t#, a#, st#, Pi#, r#
Dim i%, m%
Private Sub Command1_Click()
a = 4  'Val(Text1.Text)
m = 10 ' 2.5 * a
Pi = 4 * Atn(1)
Picture1.Width = Picture1.Height
Picture1.AutoRedraw = True
Picture1.Scale (-m, m)-(m, -m)
 
Picture1.Line (-m, 0)-(m, 0), vbBlue
For i = -m To m
  Picture1.PSet (i, 0)
  Picture1.Print i
Next i
 
Picture1.Line (0, m)-(0, -m), vbBlue
For i = -m To m
  Picture1.PSet (0, i)
  Picture1.Print i
Next i
 
st = 0.001
For t = 0 To Pi Step st
'повернутый
    r = (3 * a / Sqr(2)) * (Sin(t) ^ 2 - Cos(t) ^ 2) / (Cos(t) ^ 3 + 3 * Sin(t) ^ 2 * Cos(t))
    'или по опр.
    'r = 3 * a * Sin(t) * Cos(t) / (Cos(t) ^ 3 + Sin(t) ^ 3)
 
    x = r * Cos(t):y = r * Sin(t)
    Picture1.PSet (x, y)
Next t
End Sub
                        