VB编程,用迭代法编一函数过程f(a),求x=a的1/3次方,就是a的立方根!

Private Sub Command1_Click()
Dim x As Single,x0 As Single,x1 As Single,a As Single
a = Val(InputBox("请输入一个数a="))
If Abs(a) < 0.000001 Then
x = 0
Else
x0 = a / 2
x1 = (2 / 3 * x0) + a / (3 * x0 ^ 2)
Do While Abs(x1 - x0) > 0.00001
x0 = x1
x1 = (2 / 3 * x0) + a / (3 * x0 ^ 2)
Loop
x = x1
End If
Print a & "的立方根为;"; x
End Su

Xa = 3
Do
Xb = Val((2 / 3) * Xa + 27 / 3 * (Xa) ^ 2)
Xa = Xb
Loop Until Abs(Val(Xb - Xa)) < 0.00001
Print "27的立方根为："; Xa
这不是我写的,求参考和改进,谢谢啦

我也求这道题的答案 呜呜呜