Equations and results involving double angle formulae

1. I would like to know if this is correct:

where x is an element of 0 and 360 (2pi in radians)

2. I would like to know where to continue in this question:

...I don't really know where to go from here and how to find angles for x.

3. I am being introduced to product and sum formulas and I don't know how to tackle the questions.

eg1.

Find the exact value of sin2x, cos2x.

The extra formulas given for sinx and cosx are:

and

I know all the normal ones like sin2x=2sinxcosx etc., just not how to apply them.

If you could help me out here that would be great :D