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If ω is a complex cube root of unity, find the value of (1 − ω − ω2)3 + (1 − ω + ω2)3

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Question

If ω is a complex cube root of unity, find the value of (1 − ω − ω2)3 + (1 − ω + ω2)3

Sum
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Solution

Since ω is the complex cube root of unity,

ω3 = 1 and 1 + ω + ω2 = 0

∴ 1 + ω = – ω2, 1 + ω2 = – ω and ω + ω2 = – 1.

(1 − ω − ω2)3 + (1 − ω + ω2)3 

= [1 – (ω + ω2)]3 + [(1 + ω2) – ω]3

= [1 – (–1)]3 + (–ω – ω)3

= 23 + (– 2ω)3

= 8 – 8ω3

= 8 – 8(1)

= 0

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Chapter 1: Complex Numbers - Exercise 1.4 [Page 20]

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