x+1/x=2cosalpha then x^n+1/x^n=...

`x+1/x=2cosalpha` then `x^n+1/x^n=`

A

`2 ^(n) cos alpha `

B

`2^(n) cos n alpha `

C

`2i sin n alpha `

D

`2 cos n alpha `

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The correct Answer is:

D

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