Private Function ArcCos(A As Double) As Double
  'Inverse Cosine
    On Error Resume Next
        If A = 1 Then
            ArcCos = 0
            Exit Function
        End If
        ArcCos = Atn(-A / Sqr(-A * A + 1)) + 2 * Atn(1)
    On Error GoTo 0
End Function

Private Function ArcSin(x As Double) As Double
  'Inverse Sine
    On Error Resume Next
        ArcSin = Atn(x / Sqr(-x * x + 1))
    On Error GoTo 0
End Function
 
Private Function ArcTan(x As Double) As Double
  'Inverse Tangent
    On Error Resume Next
        ArcTan = Atn(x) * (180 / Pi)
    On Error GoTo 0
End Function