Yes, that is fine. It doesn't matter when or how you found out the answer to the question, either. If you simply want to impart knowledge, then you can post a relevant question then immediately answer it with that knowledge.
However, in doing so you should bear in mind the following things:
- If it becomes obvious you're doing this only to accumulate points, then we will step in and remove the posts.
- We'll ask you to slow down if you post too many questions like this at once. We want to keep questions where the asker doesn't know the answer toward the top of the navigation.
- Other people may also answer the question. Their answers could be better than yours, and in that case, you should select the best answer fairly.
- Make sure what you're posting is thorough, and of good quality. You should know what you're talking about if you're going to do this (like with any other answer).
- You will not receive the +20 points for having the best answer if you were also the author of the question.