Quadratic solutions of polynomial functional equations

Abstract The so-called polynomial equations play an important role both in algebra and in the theory of functional equations. If the unknown functions in the equation are additive, relatively many results are known. However, even in this case, there are a lot of open questions. In some specific cases, according to classical results, the unknown additive functions are homomorphisms, derivations, or linear combinations of these. The question arises as to whether the solutions can be described even if the unknown functions are not assumed to be additive but to be generalized monomials. As a starting point, in this paper, we will deal with quadratic functions. We aim to show that quadratic functions that are solutions to certain polynomial equations necessarily have a ‘special’ form. Further, we also present a method to determine these special forms.