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Let alpha ,beta denote the cube roots of...

Let `alpha ,beta` denote the cube roots of unity other than 1 and `alpha ne beta` let `S=underset(n=0)overset302sum(-1)^n(alpha/beta)^n` then the value of S is

A

either `-2omega or -2omega^2`

B

`either (-2omega)or 2omega^2`

C

either `2omega or (-2omega^2)`

D

either`2omega or 2omega^2`

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The correct Answer is:
A
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