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

> 
> "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: 
1. You have no way of knowing if the answer will truly be useless to the one asking the question.
2. "killing an ant with a nuclear bomb" So what? Is it a bad thing?
3. Answers are for everyone, not just the OP. Maybe these answers will be helpful to someone else. Considering that questions get closed for being duplicate of one another, if someone asks a question about some limit but displays high-school level knowledge, does it mean that everyone is forbidden from ever answering this limit using power series on this site?
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.