Grace–Walsh–Szegő theorem

The Grace–Walsh–Szegő theorem is a significant result in complex analysis and polynomial theory, particularly concerning the behavior of polynomials and their roots. The theorem deals with the location of the roots of a polynomial \( P(z) \) in relation to the roots of another polynomial \( Q(z) \). Specifically, it provides conditions under which all roots of \( P(z) \) lie within the convex hull of the roots of \( Q(z) \).