Quote Originally Posted by Freaky-Person View Post
They're not. We have some identites but not these ones. All we have is 8 of the easiest ones. Anything multiplied or divided by two, or even associated with the angles is in the AP or Pre-calculus course. This is Canada for you...
Some of these are relatively trivial results of the sum and difference identities:


Put A=B:


then using Pythagoras's theorem in the form:


we get:




and by putting a=2A