I'm looking for a general approach (or approaches) for finding the roots of polynomials with rational coefficients of higher degrees than $4$. The problem is that I need to find the exact roots and not their approximations. And also I need to find both real and complex roots.
I know that there are no methods which will work for every polynomial, but I need to find at least several methods which will work for $5$ or $6$ degree.
Could anyone please suggest a link or a book where this topic is discussed?