求教VB黄金分割法求最值，不知道哪里出问题了 大神帮帮忙看看谢谢

Public Function f(x As Long) As Long              '定义程序f
i = Val(Text2.Text)
f = (0.8 - ((1 + Sqr(i * x)) / (0.97 * x * (i + Sqr(i * x)))) ^ (1 / 3) * x) ^ 2
End Function

Private Sub Command1_Click()

Dim m As Long, n As Long, a As Long, b As Long, fm As Long, c As Long
Dim fa As Long, fb As Long, q As Long
a = 1#                                       '一级和二级传动比的比值取1~1.7
b = 1.7
q = 0.259
m = 1.2674
n = 1.4326
Do While (q > 0.01)                            '精度要求为0.01
    m = a + 0.382 * (b - a)
    n = a + 0.618 * (b - a)
    q = (n - m) / (b - a)
    If fm >= fn Then                            '新的搜索区间
       a = a
       b = n
    ElseIf fm < fn Then                         '新的搜索区间
       a = n
       b = b
    End If
    Loop
    c = (a + b) / 2                       '取中点值
   Text1.Text = c
End Sub