We study connections between self-inversive and self-reciprocal polynomials, reduction theory of binary forms, minimal models of curves, and formally self-dual codes. We prove that if X is a superelliptic curve defined over C and its reduced automorphism group is nontrivial or not isomorphic to a cyclic group, then we can write its equation as y n = f (x) or y n = xf (x), where f (x) is a self-inversive or self-reciprocal polynomial. Moreover, we state a conjecture on the coefficients of the zeta polynomial of extremal formally self-dual codes.arXiv:1606.03159v1 [math.CV]