Sum of cosines
Geometry
Level
5
\[A=\cos\left(\frac{13\pi}{20}\right) +\cos\left(\frac{21\pi}{20}\right) +\cos\left(\frac{29\pi}{20}\right) +\cos\left(\frac{37\pi}{20}\right) \]
Find the value of \(\lfloor 1000A \rfloor\).
\(\)
Notation: \( \lfloor \cdot \rfloor \) denotes the floor function.
by
Chan Lye Lee