(First problem) Express in terms of and
Attempt: According to de Moivre's formula - so:
de Moivre - and
After some arithmetic arrangements and and Pythagorean trigonometric identity I got this: and task under a) is completed (I think).
But the problem is at task b), so, I don't know how to write expression (1) in terms of cosx function. Is there any identity? Or maybe some other method.
(Second problem) If is a complex number, what does this equation represent:
Attempt: No attempt. I need a complete solution and explanation.