Given the Equivalence relation R = { x, y $ \in$ $ \Bbb{Z}$ : (x+y) mod 2 = 0}, what are equivalence classes of 1 and 2?

I can’t really see the equivalence classes of infinite sets. Only by having a drawing of all elements can I distinguish the answers, wich is not the case in the above mentioned example.

What would be the best way to tackle such problems?

Thanks!