You can understand how to derive them, or memorize them. Once you see the pattern, you can use the identities to:
* Merge as many trigs into one (e.g. merge sines and cosines into one)
* Split trig into two and regroup
Where can I find some type of aid with Trig Identities. I am having a real difficult time trying to solve these when given in equation form or any other problem related to solving the Identity.
PS - Thanks to all that have helped me with my trig questions.