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(1+itanθ)

^{n}+ (1-itanθ)

^{n}=2cosnθ/cos

^{n}θ

where cosθ ≠ 0

I tried to approach this by converting into modulus argument form but wasn't really sure if that was correct. It's a common New South Wales HSC question but I couldn't find a solution anywhere. Help would be greatly appreciated :)