Present derivative expression in Visual Basic

I am using the "Extreme Optimization" package to learn how to use more advanced calculus and mathematics in programs using the VB language. However, I need help with the program saving in memory and presenting the user with the non-numeric derivative of a given expression. In the case, I have for example an expression x^2 + x^5 and its derivative is 2x + 5x^4. However, when I try to present such an expression, the returned value is zero. The code is attached. I've done several modifications, but I did not succeed. So I put here the code I did initially. Thank you!

Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click

    Dim x As Double

    Dim result As Double = FunctionMath.Derivative(AddressOf Differentiation, x)

    MessageBox.Show("diferenciacao em x  = " + result.ToString, "resultado", MessageBoxButtons.OK)

End Sub

Function Differentiation(ByVal x As Double) As Double

    Return Math.Pow(x, 2) + Math.Pow(x, 5)

End Function