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If ω is a complex cube root of unity, show that (a − b) (a − bω) (a − bω2) = a3 − b3 - Mathematics and Statistics

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Question

If ω is a complex cube root of unity, show that (a − b) (a − bω) (a − bω2) = a3 − b3

Sum

Solution

ω is the complex cube root of unity

∴ ω3 = 1 and 1 + ω + ω2 = 0

Also, 1 + ω2 = − ω, 1 + ω = − ω2 and ω + ω2 = − 1

L.H.S. = (a − b)(a − bω)(a − bω2)

= (a − b) (a2 − abω2 − abω + b2ω3)

= (a − b) [a2 − ab(ω2 + ω) + b2(1)]

= (a − b) [a2 − ab(−1) + b2]

= (a − b) (a2 + ab + b2)

= a3 − b3

= R.H.S.

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Cube Root of Unity
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Chapter 1: Complex Numbers - Exercise 1.4 [Page 20]

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