A note on a generalization of the quadratic functional equation

In the present paper, we determine the solutions f : S!H of the generalized quadratic functional equation f (x+s(y))+ f (x+t(y)) = 2 f (x)+2 f (y); x;y 2 S; in terms of additive and symmetric, bi-additive maps, where S is a commutative semigroup, H is an abelian group which is uniquely 2-divisible, and s; t are two involutions of S: