I suppose you are to simplify this?
I'm not sure how much help your hint is but try this instead:
$\displaystyle sin(x + y) = sin(x) cos(y) + sin(y) cos(x)$
and
$\displaystyle cos(x + y) = cos(x) cos(y) - sin(x) sin(y)$
Give it a shot and tell us how you are doing with it.
-Dan