Oh yeah, and don't just write down "-2", it's meaningless on its own. Specify *what* equals -2 (yeah I know, in this case it's clearly y) because then you have to go and get what x is and that will probably be something completely different.

Like saying "How old are Fred and Mary?" You know Fred's 12 but you don't know Mary's age, so you say, "12." No you don't, you say "Fred's 12."