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

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=0`

Text Solution

Verified by Experts

The correct Answer is:
D
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