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Problem
Problem
If
f
′
′
(
x
)
>
0
f''(x) > 0
f
′′
(
x
)
>
0
and
f
′
(
1
)
=
0
f'(1) = 0
f
′
(
1
)
=
0
such that
g
(
x
)
=
f
(
cot
2
x
+
2
cot
x
+
2
)
g(x) = f(\cot^2 x + 2\cot x + 2)
g
(
x
)
=
f
(
cot
2
x
+
2
cot
x
+
2
)
, where
0
<
x
<
π
0 < x < \pi
0
<
x
<
π
, then the interval in which
g
(
x
)
g(x)
g
(
x
)
is decreasing is a.
(
0
,
π
)
(0, \pi)
(
0
,
π
)
b.
(
π
2
,
π
)
\left(\frac{\pi}{2}, \pi\right)
(
2
π
,
π
)
c.
(
3
π
4
,
π
)
\left(\frac{3\pi}{4}, \pi\right)
(
4
3
π
,
π
)
d.
(
0
,
3
π
4
)
\left(0, \frac{3\pi}{4}\right)
(
0
,
4
3
π
)
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