Well let's say we have the two groups G1 and G2 with operations *1 and *2, respectively, and we do the cartesian product to get
G1 x G2 = { (a,b) : a is an element of G1, and b is an element of G2} = G
with the binary operation, * let's say, defined by
(a,b) * (c,d) = (a *1 c, b *2 d)...