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Mathematics
Problem
The value of
5
⋅
cot
(
∑
k
=
1
5
cot
−
1
(
k
2
+
k
+
1
)
)
5 \cdot \cot \left( \sum_{k=1}^{5} \cot^{-1}(k^2 + k + 1) \right)
5
⋅
cot
(
∑
k
=
1
5
cot
−
1
(
k
2
+
k
+
1
)
)
is equal to a.
5
2
\frac{5}{2}
2
5
b. 7 c. -7 d.
7
2
\frac{7}{2}
2
7
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