i dont know what to do with 1/2 sin (alpha) how to simplify it with
You need to simplify
I gave you a way to expand out the
When you do so you will see what to do with the sin(a) term.
I think your biggest problem is that you are using a calculator. Put it away. If you work with exact answers you will easily see what to do.
So again I ask you: What are
and
-Dan