Question: I've seen a lot of questions of rather elementary limits (most of them 'highschool' level), where users answer saying things like

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> "Note that $\sin x =\sum \frac {(-1)^n}{(2n+1)!}x^{2n+1}$, then it's rather trivial $\dots$"
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Or

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> "Just remember that $\sqrt x \in o(x)$, then $\dots$"
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I'm always disappointed at seeing answers like that, it's utterly obvious they'll be useless for the one asking the question (and most of the times it's really kind of "killing an ant with a nuclear bomb").

What do you guys think?

Answer: 
I think such answers should not be downvoted merely because they are beyond the presumed understanding of the OP. (There may of course be other reasons to downvote the answer.) In the first place, "answers are for everyone." I can't count the number of times that I've learned something here because someone else introduced a more powerful technique than I was aware of. (Well, obviously it's *countable*, but—oh, you know what I mean.) In the second place, who can say for sure what the OP knows, or can apprehend once shown?

As for frowning upon such answers—to be sure, no one can know if you frown upon something, but in my opinion, it's not productive to censure someone (not censor) for using a sledgehammer instead of a flyswatter. My countersuggestions:

* Let the OP comment on the answer if they don't find it helpful; their feedback is more likely to elicit a positive response from the answerer than someone from the peanut gallery.
* Upvote the answers you *do* approve of, rather than downvote the one you don't.
* If no one else has provided a more elementary solution, it may behoove you to add one.
Well, I certainly frown on these sorts of answers, personally. If nothing else, they show a lack of care and sensitivity towards the OP. I sometimes leave a comment telling the author that his (or her) answer is probably useless to the OP. And in extreme cases, I downvote.

I think it's often possible to judge the OP's level of mathematical ability and sophistication from the content and phrasing of the question. Providing an answer that's clearly way over the OP's head is just plain rude (to the OP), in my view.

I also think the "answers are for everyone" argument is a weak excuse for overly abstract or sophisticated answers. The more knowledge you assume, the less accessible the answer. Not just to the OP, but to everyone.