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Problems
If
f
(
x
)
=
∑
r
=
1
n
tan
−
1
(
1
x
2
+
(
2
r
−
1
)
x
+
(
r
2
−
r
+
1
)
)
f(x) = \sum_{r=1}^{n} \tan^{-1} \left( \frac{1}{x^2 + (2r-1)x + (r^2 - r + 1)} \right)
f
(
x
)
=
∑
r
=
1
n
tan
−
1
(
x
2
+
(
2
r
−
1
)
x
+
(
r
2
−
r
+
1
)
1
)
…
Mathematics
Problem
If
f
(
x
)
=
∑
r
=
1
n
tan
−
1
(
1
x
2
+
(
2
r
−
1
)
x
+
(
r
2
−
r
+
1
)
)
f(x) = \sum_{r=1}^{n} \tan^{-1} \left( \frac{1}{x^2 + (2r-1)x + (r^2 - r + 1)} \right)
f
(
x
)
=
∑
r
=
1
n
tan
−
1
(
x
2
+
(
2
r
−
1
)
x
+
(
r
2
−
r
+
1
)
1
)
, then
lim
n
→
∞
f
′
(
0
)
\lim_{n \to \infty} f'(0)
lim
n
→
∞
f
′
(
0
)
is a. 1 b. 2 c. 3 d. 4
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