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Mathematics
Mathematics
Problem
The value of
∑
k
=
1
6
(
sin
(
2
π
k
7
)
−
i
cos
(
2
π
k
7
)
)
\sum_{k=1}^{6} \left( \sin \left( \frac{2\pi k}{7} \right) - i \cos \left( \frac{2\pi k}{7} \right) \right)
∑
k
=
1
6
(
sin
(
7
2
π
k
)
−
i
cos
(
7
2
π
k
)
)
, where
i
=
−
1
i = \sqrt{-1}
i
=
−
1
, is a.
−
1
-1
−
1
b. 0 c.
−
i
-i
−
i
d.
i
i
i
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