I'm a bit rusty on my trig as well, but maybe the above can help you. Got that errant cosine that you somehow need to manipulate. Work from the left hand side, and see if you get to any of the steps I did on the right hand side.
Is the problem written correctly? I'm willing to bet there is no error in the book you are using (or rather there might be, but the likelihood that we're working out a problem that is isn't too high).
Is the problem written correctly? I'm willing to bet there is no error in the book you are using (or rather there might be, but the likelihood that we're working out a problem that is isn't too high).
I believe its an error in the book because its written like that. Thank you for your help and I'll let you go because I feel like I'm bothering you too much. Thank you again(: