'Return postprocessed roots of specified kind.'

@classmethod
def _get_roots(cls, method, poly, radicals):

    if (not poly.is_univariate):
        raise PolynomialError('only    univariate    polynomials    are    allowed')
    (coeff, poly) = cls._preprocess_roots(poly)
    roots = []
    for root in getattr(cls, method)(poly):
        roots.append((coeff * cls._postprocess_root(root, radicals)))
    return roots
