Public Function Sec(ByVal X As Double) As Double
    Sec = 1 / Cos(X)
End Function

Public Function Cosec(ByVal X As Double) As Double
    Cosec = 1 / Sin(X)
End Function

Public Function Cotan(ByVal X As Double) As Double
    Cotan = 1 / Tan(X)
End Function

Public Function Arcsin(ByVal X As Double) As Double
    Arcsin = Atn(X / Sqr(-X * X + 1))
End Function

Public Function Arccos(ByVal X As Double) As Double
    Arccos = Atn(-X / Sqr(-X * X + 1)) + 2 * Atn(1)
End Function

Public Function Arccotan(ByVal X As Double) As Double
    Arccotan = Atn(X) + 2 * Atn(1)
End Function