Fake injury
Sometimes, knowing the answer isn’t the hard part. The hard part is to sneak it into the classroom without looking suspicious. You need to find white surfaces that can take the place of a cheat sheet. Here we have a clever example.

You can fake an injury and use a band-aid to cover it up. If you haven’t noticed, they are entirely white on the inside. Perfect for writing one or two answers on it. We can assure you that no teacher will ask to take a look at your injury.