The tooltip on a downvote button reads
This question does not show any research effort; it is unclear or not useful
If your opinion of a question is “this guy should do his own homework instead of dumping it on us”, that's a prime case of “does not show any research effort”, and a downvote is perfectly consistent with the guidelines.
As per our homework policy, homework questions are accepted. But a dump of a homework assignment is often not a suitable Stack Exchange question. The usual quality control applies. A dump of a homework assignment may often be closed as
- too broad, if the exercise is not a straightforward question and requires a lengthy discussion or solving multiple subproblems.
- unclear what you're asking, if the homework problem is simply copied and the asker does not specify which part is giving him/her trouble.
Please leave a comment in such cases, like D.W. did (of course if someone already left a comment and you're happy with it then you don't need to leave your own). Part of the comment should be some generic, polite “tell us what you've done so far”, and part of it should ask a few more specific questions suggesting what avenues to explore first.