Test the Following Series for Convergence or Divergence $\sum _ { n = 1 } ^ { \infty } ( - 1 ) ^ { n } \cos \left( \frac { \pi } { n } \right)$

Short Answer

Test the following series for convergence or divergence: $\sum _ { n = 1 } ^ { \infty } ( - 1 ) ^ { n } \cos \left( \frac { \pi } { n } \right)$ .