A new type of functional equations on semigroups with involutions

Abstract

Let $S$ be a commutative semigroup, $K$ a quadratically closed commutative field of characteristic different from $2$, $G$ a $2$-cancellative abelian group and $H$ an abelian group uniquely divisible by $2$. The aim of this paper is to determine the general solution $f:S^2\to K$ of the d'Alembert type equation: $$f(x+y,z+w)+f(x+\sigma (y),z+\tau (w))=2f(x,z)f(y,w),(x,y,z,w\in S)$$ the general solution $f:S^2\to G$ of the Jensen type equation: $$f(x+y,z+w)+f(x+\sigma (y),z+\tau (w))=2f(x,z),(x,y,z,w\in S)$$ the general solution $f:S^2\to H$ of the quadratic type equation quation: $$f(x+y,z+w)+f(x+\sigma (y),z+\tau (w))=2f(x,z)+2f(y,w),(x,y,z,w\in S)$$ where $\sigma ,\tau :S\to S$ are two involutions.