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Mathematics
Problem
Prove that,
cos
4
π
8
+
cos
4
3
π
8
+
cos
4
5
π
8
+
cos
4
7
π
8
=
3
2
\cos^4 \frac{\pi}{8} + \cos^4 \frac{3\pi}{8} + \cos^4 \frac{5\pi}{8} + \cos^4 \frac{7\pi}{8} = \frac{3}{2}
cos
4
8
π
+
cos
4
8
3
π
+
cos
4
8
5
π
+
cos
4
8
7
π
=
2
3
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