Complex De Moivre's & Trig Question (1 Viewer)

pixiefeathers

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Hi, I attempted part b of this question (Cambridge X2 Exercise 3B Q14) and thought I got the answers but they were incorrect. I think I got it wrong when I equated 8θ = 0, π, 2π, etc. but I'm not sure. Would someone be able to tell me how I went wrong? I have attached my solutions and the actual solutions. I'd really appreciate some help, thanks.

Question:
1674781666871.png

My solution (part a is correct):
1674781929270.jpg


Cambridge solution:
1674781789490.png
 

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pixiefeathers

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Thank you! Is it that when I solve sin8θ = 0, I should always put 8θ = ±π, ±2π, ±3π, etc., instead of π, 2π, 3π, 4π, etc.? Because I seem to only be able to get the correct answers if I put the former not the latter.
 

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pixiefeathers

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Right, I will remember to test those first. Thank you so much for your help!
 

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