In academic writing, and in most QualityGal freelance writing work, rhetorical questions are not appropriate. A rhetorical question is one for which no answer is required or expected. These are used in written text when the writer assumes that the individual reading the content will know the answer, or the writer continues on to answer the question in the content. In content such as ours points can be made more clearly when the information alluded to in the question is included as a statement. By asking a question the reader may or may not know the answer to, you run the risk of your point not actually being made.
[Note: We now have an updated take on this topic here: You might want to give it a look.]