Yes, it was very helpful, I understood Guest's guidelines but I want to also thank you for providing the full steps and working out.
Since the both of you took the time to help me out I hope I won't be an annoyance by asking how exactly you arrived at this part:
LetR[cos(2x+θ)]=4.4cos(2x)−20sin(2x)
A similar identity that I know of is A*sin(x) + B*cos(x) = C*sin(x+v) where tan(v) = b/a
Also, based on the answer you provided and plugging in C it ended up incorrect.