Did I make a mistake here somewhere? The solution in the back of the book is completely different. Seems like they used trig sub one step later or something. I can't find any error in my logic. Test coming up soon and I'm confused and panicking -_-!
Actually I just found a mistake with my constants! But apart from that, is it correct? The first term should be multiplied with -1/2 and the second with 3/2.