def get_beta_y_cubic(x, mu):
    """
    Evaluation of cubic polynomial form of LBCCs.
    Solutions are pinned at Beta(mu=1)=1 and y(mu=1)=0.
    :param x: parameter values as list/list-like
    :param mu: value of mu
    :return: Beta and y
    """
    beta = 1. - (x[0] + x[1] + x[2]) + x[0] * mu + x[1] * mu ** 2 + x[2] * mu ** 3
    y = -(x[3] + x[4] + x[5]) + x[3] * mu + x[4] * mu ** 2 + x[5] * mu ** 3

    return beta, y