# Solve it in Friday 13th - part 2

Geometry Level 3

$$\cos\left(\dfrac{2\pi}{13}\right)\cos\left(\dfrac{6\pi}{13}\right)+\cos\left(\dfrac{2\pi}{13}\right)\cos\left(\dfrac{8\pi}{13}\right)+\cos\left(\dfrac{6\pi}{13}\right)\cos\left(\dfrac{8\pi}{13}\right)$$

If the trigonometric expression above can be expressed as $$-\dfrac{\alpha}{\beta}$$ for coprime positive integers $$\alpha$$ and $$\beta$$, find the value of $$\alpha+\beta$$.

See Part 1 and Part 3.

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