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If α and β are complex cube roots of unity, prove that (1 − α)(1 − β) (1 − α2)(1 − β2) = 9. - Mathematics and Statistics

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Question

If α and β are complex cube roots of unity, prove that (1 − α)(1 − β) (1 − α2)(1 − β2) = 9.

Sum
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Solution

Since α and β are the complex cube roots of unity, α2 = β and β2 = α

Also, α3 = 1, 1 + α + α2 = 0

∴ α4 = α3.α = α, 1 + α2 = – α and 1 + α = – α2

∴ (1 – α)(1 – β)(1 – α2)(1 – β2)

= (1 – α)(1 – α2)(1 – α2)(1 – α)

= (1 – α)2(1 – α2)2

= (1 + α2 – 2α)(1 + α4 – 2α2)

= (1 + α2 – 2α)(1 + α – 2α2)        ...[∵ α4 = α]

= (– α – 2α)(– α2 – 2α2)

= (– 3α)(– 3α2)

= 9 α3

= 9 × 1

= 9

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Cube Root of Unity
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Chapter 1: Complex Numbers - Miscellaneous Exercise 1.2 [Page 22]

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Balbharati Mathematics and Statistics 2 (Arts and Science) [English] Standard 11 Maharashtra State Board
Chapter 1 Complex Numbers
Miscellaneous Exercise 1.2 | Q II.18 | Page 22

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