def get_bd(r, a):
    """
    Converts turnover and relative extinction to birth and death rates.

    Args:
        r (float): turnover or net diversification (birth - death)
        a (float): relative extinction (death / birth)

    Returns:
        (float, float): birth, death
    """
    return -r / (a - 1), -a * r / (a - 1)