Wait, that's not helpful. What do you mean?
Let's start with competence. To encourage your child to do homework on his own, make him feel like he can do it. Tell him he can multiply fractions and get him to say aloud that he can do it.
Ernest Dempsey, who has been a school counselor for 10 years in Tennessee, encourages parents to play a game with their kids called "Make the Student the Teacher." He says parents should, "sit down and ask the child to show them what they learned at school that day."
If you push your child to teach you material from school, you will prove that he is a capable student. If you're working on a difficult subject, it's up to you to highlight the things your child does well. Applaud when he doesn't give up or when he does better than the time before.