Ratio TestIn Probability, Lโกlimโกnโโโฃan+1anโฃL \equiv \lim_{n \to \infty} |{a_{n+1} \over a_n}|Lโกnโโlimโโฃanโan+1โโโฃ $L < 1$: Series converges absolutely. $L > 1$: Series diverges. $L = 1$: Test fails.