Hi

Here are some of the questions I'm stuck on.

1)Simply the expression:

this is what i have done and i cannot see where i have gone wrong.

answers says its cos(-y).why?

2)express sin(3x) in terms of sin(x). This questions follows on from the previous question which was asking to expand sin(x+2x) answer to this is .

3)Use the compound angle formulas and appropriate angles to find the exact value of .

This is what i have done:

book's answer is