MHB Limit Comparison Test: Does L Approaching Infinity Matter?

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The limit comparison test indicates that if L approaches infinity, the divergence of the series is still valid. Specifically, if both sequences a_n and b_n are positive and L = lim (n→∞) a_n/b_n = ∞, then if the series ∑b_n diverges, ∑a_n will also diverge. However, if ∑b_n converges, an example with a_n = 1 and b_n = 1/n^2 shows that ∑a_n can still diverge. The discussion emphasizes the importance of testing various examples to confirm the rule's applicability. Overall, the limit comparison test remains a reliable method for determining series convergence and divergence.
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The limit comparison test states that if $a_n$ and $b_n$ are both positive and $L = \lim_{{n}\to{\infty} } \frac{a_n}{b_n} > 0$ then $\sum_{}^{} a_n$ will converge if $\sum_{}^{} b_n$ and $\sum_{}^{} a_n$ will diverge if $\sum_{}^{} b_n$ diverges. Does this rule also apply if $L$ diverges to infinity?
 
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Take an example for $a_n,b_n$ and see if the rule satisfies.
 
ZaidAlyafey said:
Take an example for $a_n,b_n$ and see if the rule satisfies.

It seems to be true based on the examples I've tried, but I'm not sure if I've tried enough examples.
 
If $a_n>0$ and $b_n>0$, $\lim_{n\to\infty} \frac{a_n}{b_n}=\infty$ and $\sum b_n$ diverges, then $\sum a_n$ also diverges. But for the case when $\sum b_n$ is convergent, take $a_n=1$ and $b_n=1/n^2$.