Visual Basic - Como se hace para que Visual Basic 5 reconozca arccosine?

Function ArcSin(X As Double) As Double

    ArcSin = Atn(X / Sqr(-X * X + 1))

End Function

Function ArcCos(X As Double) As Double

    ArcCos = Atn(-X / Sqr(-X * X + 1)) + 2 * Atn(1)

End Function

Private Sub Command1_Click()

    ' remplaza el valor 0.5 con el grado (en radians) que quieras calcularle el ArcSin y el ArcCos

    MsgBox "ArcSin(0.5) = " & ArcSin(0.5)

    MsgBox "ArcCos(0.5) = " & ArcCos(0.5)

End Sub