Sequence satisfying a condition for all n

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Homework Help Overview

The discussion revolves around a sequence of positive numbers {s_n} that satisfies the condition s_(n+1) > αs_n for all n, where α > 1. Participants are tasked with demonstrating that s_n approaches infinity as n increases.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the implications of the inequality by comparing terms in the sequence, such as s_2 to s_1 and s_3 to s_2. There is a discussion about the relationship to geometric sequences and the use of logarithms to analyze growth. Questions arise regarding the connection between the sequence's behavior and the concept of limits.

Discussion Status

The discussion is ongoing, with participants sharing their thoughts on how to approach the problem. Some guidance has been offered regarding comparisons between terms, but there is no explicit consensus on the best method to proceed.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information they can use or the methods they can apply. There is also a mention of a limit condition related to convergence that is being questioned in the context of the problem.

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Homework Statement



Suppose that a sequence {s_n} of positive numbers satisfies the condition s_(n+1) > αs_n for all n where α > 1. Show that s_n → ∞

My teacher mentioned something about making it into a geometric sequence and taking the log. I'm just confused.

Homework Equations





The Attempt at a Solution

 
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You can start with s2 > as1. Now what about s3? Can you compare it to s2 and s1? Continue...
 
StarTiger said:

Homework Statement



Suppose that a sequence {s_n} of positive numbers satisfies the condition s_(n+1) > αs_n for all n where α > 1. Show that s_n → ∞

My teacher mentioned something about making it into a geometric sequence and taking the log. I'm just confused.

Homework Equations





The Attempt at a Solution

So [itex]s_2> a s_n[/itex], [itex]s_3> a s_2> a(a s_1)= a^2 s_1[/itex], [itex]s_4> a s_3> a(a^2 s_1)= a^3 s_1[/itex]. So [itex]s_n>[/itex] a to what power times [itex]s_1[/itex]? What does that have to do with a "geometric sequence"?
 
If [tex](s_n)[/tex] is a sequence and the limit [tex]\lim_{n \to \infty}|s_{n+1} / {s_n}| = L[/tex] exists and [tex]L < 1[/tex], then [tex]\lim s_n[/tex] converges. If not, what do you think happens?
 

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