Which condition is sufficient to claim that ∑n=1∞an\sum_{n=1}^{\infty} a_n∑n=1∞an converges?
limn→∞an=0\lim_{n \to \infty} a_n = 0limn→∞an=0
∑n=1∞∣an∣\sum_{n=1}^{\infty} |a_n|∑n=1∞∣an∣ converges
limn→∞an+1an=1\lim_{n \to \infty} \frac{a_{n+1}}{a_n} = 1limn→∞anan+1=1
ana_nan is a decreasing sequence