# Summation + Trigonometry

Geometry Level 3

$\large\sum _{n=1}^{18} \cos ^{ 2 }(5n^{\circ})$

Find the value of the summation above.

If the answer is of the form $\frac{a}{b}$, where $a$ and $b$ are positive coprime integers, find $a+b$.

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