Вычислить корень уравнения - VB

Function root(x As Double, eps As Double) as Double
      xp# = x
      Do
        xc# = xp# - (xp# ^ 4 + 2 * xp# ^ 2 - xp# - 1) / (4 * xp# ^ 3 + 4 * xp# - 1)
        If Abs(xc# - xp#) <= eps Then Exit Do
        xp# = xc#
      Loop
      root = xc#
End Function
 
Sub Test()
 
    x# = root(0, 0.00001)
 
    Debug.Print x#
    Debug.Print x# ^ 4 + 2 * x# ^ 2 - x# - 1
 
End Sub