The main way to spot Difference of Squares is that there's no middle term. Once identified, you'll make quick work of gems like x2-16, x2 - 4, and y2-1.
OOPS! To create playlists you must logged in.
If you do not have an account, you should get one, because it is awesome! You can save a playlist for each test or each chapter, and save your "greatest hits" into a "watch right before the final" list (not that we recommend cramming, but when in Rome...)