Why did my answer get downvoted?

I recently took out the time to provide a very comprehensive solution to a calculus problem, but surprisingly ended up losing reputation because of it. Could I get some feedback regarding what makes my answer worthy of a negative score so that in future I can steer clear of those red flags?

Indefinite integral (calculus)

• As postmortes' answer says, the question is basically a PSQ (problem statement question). As I write this, it has $4$ close votes, so it just needs $1$ more to be closed. If so, it may also possibly later be deleted. I've seen a few other cases where what seems to be reasonably good answers to PSQ's are downvoted but, as stated below, you can never be sure unless the downvoter leaves a comment as to why they downvoted. – John Omielan May 6 '19 at 17:32
• I suggest working on problems that interest you, enough so that what you learn from working on them (or from explicating them) outweighs the consideration of reputation "points". – hardmath May 7 '19 at 0:02