def tau3_from_mass1_mass2(mass1, mass2, f_lower):
    r"""Returns :math:`\tau_3` from the component masses and given frequency.
    """
    mtotal = mass1 + mass2
    eta = eta_from_mass1_mass2(mass1, mass2)
    return tau3_from_mtotal_eta(mtotal, eta, f_lower)