You are doing just about everything wrong! If there is more than one sub-forum you feel a problem could be in, choose one. Do not double post. And you have shown no work of your own. I presume you would prefer hints to help YOU answer the question rather than just being given the answer- and we need to see where you have trouble to offer hints and help.
What, exactly, does DeMoivres' theorem say and how is it relevant to this problem?