I’m stuck on the following problem (see Attachment) any help would be greatly appreciated
trig identities 2.rtf
I’m not sure how it goes from here to the next line
(I rearranged the factors in the last term to make it consistent.)
Distribute the 2:
Note that each term begins with or . Recall the sine of a double angle identity: So
, and the same for angle phi.
Use the Pythagorean identity: