# Soviet Russian Cosine #2

Geometry Level 3

If the exact value of $$\displaystyle\cos\frac{2\pi}{7}+\cos\frac{4\pi}{7}+\cos\frac{6\pi}{7}$$ can be represented in the form $$\displaystyle\frac{(-a)\sqrt{b}}{c}$$, and $$gcd(a, b, c) = 1$$, then find $$a+b+c$$.

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