  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: $$ f(x+y,z+w)+f(x+\sigma(y),z+\tau(w)) =2f(x,z)f(y,w),\quad\quad
(x,y,z,w\in S) $$ the general solution $f:S^2\to G$ of the Jensen type
equation: $$ f(x+y,z+w)+f(x+\sigma(y),z+\tau(w)) =2f(x,z),\quad\quad
(x,y,z,w\in S) $$ the general solution $f:S^2\to H$ of the quadratic type
equation quation: $$ f(x+y,z+w)+f(x+\sigma(y),z+\tau(w))
=2f(x,z)+2f(y,w),\quad\quad (x,y,z,w\in S) $$ where $\sigma,\tau: S\to S$ are
two involutions.
