1) Triangle inequality, which here is just an absolute value game.
2) Notice the word "could". That's different than "is always"/"necessarily"/"implies"/etc.. It could be a special cases, but even so, it *could* be a valid solution.
3) Draw things to extremes, and not that only two possible extremes exist in these scenarios. Extremes often clarify things I think - and when you're hunting for what *could* be the case, you need to allow for things to be as extreme as possible.