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Mathematics
Mathematics
Problem
Evaluate
∑
r
=
1
n
−
1
cos
2
(
r
π
n
)
\sum_{r=1}^{n-1} \cos^2 \left( \frac{r\pi}{n} \right)
∑
r
=
1
n
−
1
cos
2
(
n
r
π
)
.
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