在界面放一个文本框，用来输入关于x的函数，这个函数的正确性必须用户自己保证，很难（不是不能）用vb来检测。
然后参照一下内容自己制作：
界面三按钮两文本框。代码为
Public X As Boolean

Private Sub Command1_Click()
Text2 = 计算(Text1)
If X Then Text2 = "你的算式有问题，请注意查对！"
Command1.Default = False
Command2.Default = True
End Sub

Function 计算(ByVal 代数式 As String) As Double
Dim OBJ As Object
On Error GoTo 错误代码
X = False
Set OBJ = CreateObject("MSScriptControl.ScriptControl")
OBJ.Language = "vbscript"
计算 = OBJ.Eval(代数式)
Set OBJ = Nothing
Exit Function

错误代码:
X = True
End Function

Private Sub Command2_Click()
Text1 = ""
Text1.SetFocus
End Sub

Private Sub Command3_Click()
End
End Sub

Private Sub Form_Load()
Command1.Caption = "计算"
Command1.Move 600, 1680, 1215, 495
Command2.Caption = "输入算式"
Command2.Move 600, 600, 1215, 495
Command3.Caption = "关闭"
Command3.Move 6000, 2500, 1215, 495
Text1 = ""
Text1.FontSize = 20
Text1.Move 2000, 600, 5000, 495
Text2 = ""
Text1.FontSize = 20
Text2.Move 2000, 1680, 5000, 495
Me.Move (Screen.Width - 8000) / 2, (Screen.Height - 4000) / 2, 8000, 4000
End Sub

Private Sub Text1_Change()
Command1.Default = True
End Sub