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Mathematics
Mathematics
Problem
If
f
(
x
)
=
cos
x
⋅
cos
2
x
⋅
cos
4
x
⋅
cos
8
x
⋅
cos
16
x
f(x) = \cos x \cdot \cos 2x \cdot \cos 4x \cdot \cos 8x \cdot \cos 16x
f
(
x
)
=
cos
x
⋅
cos
2
x
⋅
cos
4
x
⋅
cos
8
x
⋅
cos
16
x
, then
f
′
(
π
4
)
f'\left(\frac{\pi}{4}\right)
f
′
(
4
π
)
is a.
2
\sqrt{2}
2
b.
−
1
2
-\frac{1}{\sqrt{2}}
−
2
1
c. 1 d. None of these
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