---

Private Sub CommandButton1_Click()
    If Not IsNumeric(TextBox1.Text) Then
        MsgBox "Введите число.", vbCritical, "Ошибка ввода"
        Exit Sub
    End If

    Dim x As Double
    Dim z As Double
    
    x = CDbl(TextBox1.Text)
    
    Select Case x
        Case Is < 0
            z = Abs(x) ^ (1 / 3)
        Case 0 To 0.99999999
            z = -2 * x + (x / (1 + x))
        Case Is >= 1
            z = Abs(3 - x) / (1 + x)
    End Select
    
    TextBox2.Text = CStr(Round(z, 4))
End Sub