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Prove that cos ((2pi)/7)+ cos ((4pi)/7) ...

Prove that `cos ((2pi)/7)+ cos ((4pi)/7) + cos ((6pi)/7) = - 1/2 `

A

1

B

-1

C

`1/2`

D

`-(1)/(2)`

Text Solution

Verified by Experts

The correct Answer is:
D
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ARIHANT MATHS ENGLISH-TRIGONOMETRIC FUNCTIONS AND IDENTITIES-Exercise (Questions Asked In Previous 13 Years Exam)
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