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Mathematics
Mathematics
Problem
Prove that
cos
55
∘
+
cos
65
∘
+
cos
175
∘
=
0.
\cos 55^\circ + \cos 65^\circ + \cos 175^\circ = 0.
cos
5
5
∘
+
cos
6
5
∘
+
cos
17
5
∘
=
0.
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