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Problem
Problem
The number of solutions of the equation
cos
4
x
+
6
=
7
cos
2
x
\cos 4x + 6 = 7 \cos 2x
cos
4
x
+
6
=
7
cos
2
x
, when
x
∈
[
315
∘
,
317
∘
]
x \in [315^\circ, 317^\circ]
x
∈
[
31
5
∘
,
31
7
∘
]
is a. 0 b. 1 c. 2 d. 4
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