I'm having trouble remembering the identites from the start of the course and am now thoroughly confused haha

If somebody could help me with these questions that would be great.

1. Simplify:

$\displaystyle cos2A/(cosA+sinA)$

2. Prove:

$\displaystyle sin^2(2)A=sin^2A-sin^4A$

3. $\displaystyle sqrt(2)cos(A-(pi/4))=cosA+sinA$

4. Solve for all possible values of X:

$\displaystyle -5sin(15(x-17degrees))-3=0$

excuse my lack of math typing skills