proof by De Moivre's Theorem (in the summation of a series)?

Usman Subhani

New member
I desperately need help on the following question:
Question 11..... Part (B)
Here is a link to the relevant question paper:

http://www.xtremepapers.net/CIE/International%20A%20And%20AS%20Level/9231%20-%20Further%20Mathematics/9231_s07_qp_1.pdf

Can sm1 post the whole solution?
How to get the 2^N[5-4Cos(theta)]
How do we get cos???? If we are taking the imaginary part????
I've made every possible attempt bt to no avail. Please smbdy solve it and post it... thanx in advance!!!!
 
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