vb绘制一次、二次、对数、幂函数图形的代码，各位帮帮忙啊~~~

Private Sub Command1_Click()
'直线 y=2*x
For x = -50 To 50 Step 0.5
y = 2 * x
Picture1.PSet (x, y)
Next
End Sub

Private Sub Command2_Click()
'y=2*x^2-3*x-20
For x = -50 To 50 Step 0.05
y = 0.2 * x ^ 2 - 5 * x - 20
Picture1.PSet (x, y)
Next
End Sub

Private Sub Command3_Click()
'y=ln(x)
For x = 0.0001 To 1 Step 0.0001
y = 2 * Log(x)
Picture1.PSet (x, y)
Next
For x = 1 To 100 Step 0.01
y = 2 * Log(x)
Picture1.PSet (x, y)
Next

End Sub

Private Sub Command4_Click()
'y=1.2^x
For x = -100 To 50 Step 0.01
y = 1.2 ^ x
Picture1.PSet (x, y)
Next
End Sub

Private Sub Command5_Click()
Picture1.Cls
Picture1.Line (-100, 0)-(100, 0), vbRed
Picture1.Line (0, 100)-(0, -100), vbRed
End Sub

Private Sub Form_Load()
Picture1.Sca