Is using an answer I posted online on Math.SE considered plagiarism? To expand on the question, I recently (as in yesterday) posted a question on Math.SE and also wrote my answer in the post, claiming that my answer was wrong. One answerer pointed out that I was correct, but simply needed to do a quick deduction step, after which I edited that question with that deduction step.

So if I use this answer now in my assignment, will it be considered an academic offense? None of my university's resources are helpful at all in this regard. I'm a student in the sciences, and all the 'resources' of the university are towards arts students. I'd like a clear cut answer because informing my instructor that I posted my own interpretation of a question on an assignment is really out of the question, since I don't know if consequences exist for that.

I'm already looking for an alternative answer, but I'd like to know if using my current answer would be an academic offense. Thanks.
I'd like to know if using my current answer would be an academic offense.


It's impossible to determine this without more information about your university and course policies.  If you're honest about what happened, then I doubt you could get in a lot of trouble for this, but of course I don't know the policies and potential consequences in your case.  At my university different courses can have different policies on collaboration (regarding what's allowed and what sort of acknowledgment must be given), but they should be explained at the beginning of the semester.

If I were teaching the course, it wouldn't bother me that you got advice on this problem, since it looks like you did most of the work yourself and learned something from the feedback you received.  However, I would be unhappy that you posted the homework problem and a complete solution online, thereby making it easy for other students in the class to copy your solution if they know about math.SE.  If the grader detects several solutions with nearly the same wording as the one you submit, then you may all be accused of cheating.

If you can't find a clear statement of the relevant policies on your course or department website, then I strongly recommend asking your instructor how to handle this.  In theory that could end badly, but I don't expect it to.  Bringing it up yourself is almost certainly better than letting the instructor discover it, and it would mean you could stop worrying.