# Trigonometry for 2016

Geometry Level 3

$\large \sum_{r=1}^N \cos\left( \dfrac{2r \pi}{2N+1} \right)$

If $$N = 2016$$, the value of the summation above is equal to $$-\dfrac AB$$, where $$A$$ and $$B$$ are coprime positive integers, find $$A+B$$.

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