def double_layer_cover_reflection_coefficient(tau_1, rho_1, rho_2) -> float:
    """
    The reflection coefficient
    Equation 8.15
    :param float tau_1: the transmission coefficients of the first layer
    :param float rho_1: the reflection coefficients of the first layer
    :param float rho_2: the reflection coefficients of the second layer
    :return: The reflection coefficient
    """

    return rho_1 + (tau_1 * tau_1 * rho_2) / (1 - rho_1 * rho_2)