On the Functional Equation U_t + U_-t = V_t + V_-t in a Banach Space, volume=3, url=https://www.sjm.anubih.ba/index.php/sjm/article/view/393, DOI=10.5644/SJM.03.2.10, abstractNote= In this paper we consider commuting one-parameter groups, {U_t : t R} and {V_t : tR} of unitary operators and the functional equation U_t + U_-t = V_t + V_-t on a reflexive strictly convex Banach space with Gateaux differentiable norm. 2000 Mathematics Subject Classification. 47D03 , number=2, journal=Sarajevo Journal of Mathematics, author=Pjanić, Karmelita, year=2024, month=Jun., pages=241–248