---

Private Sub CommandButton1_Click()
    Dim x As Double
    Dim y As Double

    If TextBox1.Text = "" Then
        MsgBox "Введите X!"
        Exit Sub
    End If

    x = Val(TextBox1.Text)

    If x < -3 Then
        y = x ^ 4
    ElseIf x < 0 Then
        y = 2 * Tan(x)
    Else
        TextBox2.Text = "Нет решения"
        Exit Sub
    End If

    TextBox2.Text = y
End Sub