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Problem
Problem
f
(
x
)
=
tan
−
1
(
sin
x
+
cos
x
)
f(x) = \tan^{-1}(\sin x + \cos x)
f
(
x
)
=
tan
−
1
(
sin
x
+
cos
x
)
, then
f
(
x
)
f(x)
f
(
x
)
is increasing in a.
(
−
π
2
,
π
4
)
\left(-\frac{\pi}{2}, \frac{\pi}{4}\right)
(
−
2
π
,
4
π
)
b.
(
−
π
4
,
π
4
)
\left(-\frac{\pi}{4}, \frac{\pi}{4}\right)
(
−
4
π
,
4
π
)
c.
(
5
π
4
,
3
π
2
)
\left(\frac{5\pi}{4}, \frac{3\pi}{2}\right)
(
4
5
π
,
2
3
π
)
d.
(
−
2
π
,
−
7
π
4
)
\left(-2\pi, -\frac{7\pi}{4}\right)
(
−
2
π
,
−
4
7
π
)
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