JEE Math Practice Question
The value of $$\cos \left( {{{2\pi } \over 7}} \right) + \cos \left( {{{4\pi } \over 7}} \right) + \cos \left( {{{6\pi } \over 7}} \right)$$ is equal to :
- A.$$-$$1
- B.$$-$$$${1 \over 2}$$
- C.$$-$$$${1 \over 3}$$
- D.$$-$$$${1 \over 4}$$
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