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

`26(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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