I'd consider (b) as separate problem. Here is the trick. Let

So now you can proceed algebraically using trig identities, or geometrically and make your own right triangle. Tangent = opposite over adjacent, and so you can make a right triangle where one of the acute angles is , the opposite side is and the adjacent side is . You can use Pythagoras to find the other side. With the fully populated triangle, you can find all trig functions of . Would you know how to proceed?