In this question you may use the results z+= 2 cos € and z" + = = 2 cos no (a) Expand (z+) and simplify your answer. [4] (b) Hence express cos'e in the form a cos 70+ bcos 50+ c cos 30 + d cos 0 [2] where a, b, c and d are rational numbers. (c) Hence evaluate [3] cos'0 de. Give your answer in the form where m and n are integers. All working must be shown. Just giving the answer, even the correct one, will score no marks if this working is not seen.