Let A be a subgroup of a commutative group (G, +) and P be a quadratically closed field. We give the full description of all pairs of functions f : G → P and g : A → P such that f(x + y) + f(x − y) = 2f(x)g(y) for (x, y) ∈ G × A.
机构:
Institute of Mathematics and Computer Science, Pedagogical University of Czestochowa, PL-42-201 Czestochowa
Institute of Mathematics, Silesian University, PL-40-007 KatowiceInstitute of Mathematics and Computer Science, Pedagogical University of Czestochowa, PL-42-201 Czestochowa