I need help with c) and d) and also e).

For c) they are asking for 2θ however I don't know what they did to get 1 - 2y^2.

d) Can you please explain to me what we do with the (pi - θ)?

e) Cos is adjacent over hypotenuse. However what do we do with the inverse of cos and y?

Please help me with these problems. Thank you so much in advance.