Tuesday, 7 June 2016

analysis - If fracan+1anleqfracbn+1bn for all n, prove series properties

an and bn are sequences of non-negative terms



an+1anbn+1bn for all n



If n=1bn converges, prove that n=1an converges




If n=1an diverges, prove that n=1bn diverges



I was thinking of trying the ratio test. For the 1st part, bn converges, which implies that lim is less than or equal to 1. If it is less than 1, than the same limit for \frac{a_{n+1}}{a_n} is less than one, which implies \sum\limits_{n=1}^\infty a_n converges. But I am not sure what to do about if the limit equals 1.



Thanks for the help

No comments:

Post a Comment

real analysis - How to find lim_{hrightarrow 0}frac{sin(ha)}{h}

How to find \lim_{h\rightarrow 0}\frac{\sin(ha)}{h} without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...