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Mathematics
Problem
How many distinct solutions of
cos
x
+
cos
3
x
+
cos
5
x
=
0
\cos x + \cos 3x + \cos 5x = 0
cos
x
+
cos
3
x
+
cos
5
x
=
0
lie in the interval
[
0
,
2
π
)
[0,\,2\pi)
[
0
,
2
π
)
? a)
8
8
8
b)
10
10
10
c)
9
9
9
d)
12
12
12
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