The question Find $\nabla f(x,y)$, where $f(x,y)=10x^3-5x^2+5xy+5y^2+8$ is pretty much of a kind "please, check if I did this correctly". I have clarified a couple of confusions in comments, and after the were resolved, I have told the OP that he was correct in his solution. As he mentioned that that was exactly what he wanted to know, I just posted an answer that comments were sufficient to the OP. My reasoning: not much is to be done with this question, and it should not distract the MSE people with the lack of answer. I do recall a couple of years ago a crusade to provide such answers to questions that were answered in comments, just in order to make them complete.
Instead, my answer was downvoted and closed. To quote @amWhy, do not take claim for answering a question (by posting in an answer field) what you fail to support, which to me does not sound friendly at all, and more like borderline offensive. I honestly do not get this policy.