There are instances where a question is asked with a specification on how the user wants to approach a problem, but the answers don't follow that instruction. This question is a good example. I gave an answer, so this may be self-indulgent, but although the OP stated in the question that they needed help with induction, some answers never touched on induction. I did like those other answers, but if the question is "How do I prove this with induction?" I don't think that they can be considered answers to that question. How should questions like these be treated? Is it bad form to answer a question differently from how the OP requests?
As argued before on this question, it doesn't detract to provide an alternate approach to a proof, and I agree that it's nice to see those other answers. However, I still think that those answers are answering a slightly different question, and not the question given. On that same thread, users argued that the questioner is owed nothing and should be grateful to any answer, but I think that there is value to questions with specific restrictions.
I think that part of the problem is that users asking this question often do so because they need help with homework/classes and they'll disregard more advanced/elegant proofs for ones they can write on their homework/understand. People get annoyed if they're asked to prove something more elementarily to help that one user, and that's fair. Plus, the answer will still be of use to users who have the necessary background. Regardless of the intent of the OP, though, I'd argue that these types of questions are still valid, because it's useful to see an elementary proof or just see a different method. Can a question like "How to prove this using x?" be treated as just "How to prove this?"?