Hi i am struggling to get this proof to work.

(1+i)^n + (1-i)^n = 2^ (n/2)+1 * cos nPi/4

n being any natural number.

I have assuming i would have to convert the LHS into polar form r(cos(theta) + isin(theta)) to end up with a multiply on the RHS.

Any help in dealing with this question would be greatly appreciated. Thank you