Sum of cosines

Geometry Level 4

\[A=\cos\left(\frac{13\pi}{20}\right) +\cos\left(\frac{21\pi}{20}\right) +\cos\left(\frac{29\pi}{20}\right) +\cos\left(\frac{37\pi}{20}\right) \]

Find the value of \(\lfloor 1000A \rfloor\).

\(\)
Notation: \( \lfloor \cdot \rfloor \) denotes the floor function.

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