Alternative Jensen type functional equation

Abstract

Let X and Y be linear spaces over a field F where F = Q,R or C and let f : X-> Y be arbitrary function. Given a constant p R such that p # 0,1, we prove that the alternative Jensen type functional equation pf(x)+(1-p) f (y) = -+f(px+ (1-p)y) is equivalent to the Jensen type functional equation pf(x)+(1-p) f (y) = -+f(px+ (1-p)y) Moreover, we prove that the general solution when p Q is f(x) = A(x) + c where A : X -> Y is an additive function and c Y