Simplify
\[\cos \frac{2 \pi}{13} + \cos \frac{6 \pi}{13} + \cos \frac{8 \pi}{13}.\]
Question:
Simplify
\[\cos \frac{2 \pi}{13} + \cos \frac{6 \pi}{13} + \cos \frac{8 \pi}{13}.\]
Answer:
Let's think step by step.

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\frac{\sqrt{13} - 1}{4}
Simplify
\[\cos \frac{2 \pi}{13} + \cos \frac{6 \pi}{13} + \cos \frac{8 \pi}{13}.\]
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