为什么这个vb.6 ln（x）代码不能用于大于2的数字？

Question

我为ln做了这个代码作为家庭作业，但它不适用于大于2的数字！

If Val(txt.Text) <= 0 Then
  MsgBox "can't find ln !", vbExclamation + vbOKOnly, "ERROR": Exit Sub
Else
  sign = -1 
  Sum = x - 1
  r = 2

  For j = 2 To 3 Step 0
    t = sign * ((x - 1) ^ r / r)

    If Abs(t) >= 0.0000001 And Abs(t) <= 100000000# Then
      Sum = Sum + t
      sign = -sign
      r = r + 1
    Else
      GoTo 12
    End If
  Next
End If

这是等式的图像：

Answer 1

非常感谢你的帮助，特别是MarkL，我做到了！而且我很高兴这个：）

如果您有兴趣，这里是最终代码^ _ ^：

        If Val(txt.Text) <= 0 Then
        MsgBox "can't find ln !", vbExclamation + vbOKOnly, "ERROR"
         Exit Sub

        ElseIf x < 0.51 Then
        sign = -1
        Sum = x - 1

        For i = 2 To 500
        t = sign * ((x - 1) ^ i / i)
        If Abs(t) >= 0.0000001 Then
        Sum = Sum + t
        sign = -sign
        Else
        GoTo 12
        End If
        Next

        Else
        Sum = 0
        For i = 1 To 600
        t = ((x - 1) / x) ^ i
        If Abs(t) < 10000000 Then
        Sum = Sum + (t / i)
        Else
        GoTo 12
        End If
        Next
        End If