爲什麼這個vb.6 ln（x）代碼不起作用？

Question

我爲ln做了這段代碼作爲作業，但它不適用於大於2的數字！ 你能幫助我嗎？

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 

這裏的方程的圖像：

Answer 1

非常感謝您的幫助，特別是MarkL，我做到了！我很高興這個:)

這裏是最終的代碼，如果你有興趣^ _ ^：

 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