Ratio Test

Consider series $\sum _{n=1}^{\mathrm{\infty }}{a}_n$ and $\underset{n\to \mathrm{\infty }}{lim}\frac{|a_{n+1}|}{|a_n|}=L$

1. If $L<1$, series is absolutely convergent
2. If $L>1$, then the series is divergent (For the original series)
3. If $L=1$, then inconclusive