If A= sum (r=1)^(3)"cos"(2r pi)/(7) and...

If `A= sum _(r=1)^(3)"cos"(2r pi)/(7) and B=sum_(r=1)^(3)"cos"(2^(r )pi)/(7)`, then :

A

`A+B=0`

B

`2A+B=0`

C

`A+2B=0`

D

`A=B`

Text Solution

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The correct Answer is:

D

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