Apart from low degree polynomials (2, 3, and 4) and factoring to lowest degrees, what are the method(s) used to find all the roots of a high-degree polynomial equations having only complex roots, and cannot be factored into lower degree polynomials?
In other words, what is the general method Computer Algebra systems (e.g. Maple, Mathematica) use to give you all the roots of polynomials equations?