This is my first post. Up until this point I have been able to figure out things by myself but these trig identities are killing me. The ones in my textbook I can figure out but the identities my teacher gives are not as clear to me. Here is the one I am I currently stuck on.
I'm not sure where to start. Perhaps the right side?
I hope I formatted it right. I don't know how to make it look pretty.
Thanks for any help!