Finding convergence of a recursive sequence

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Homework Help Overview

The discussion revolves around the convergence of a recursive sequence defined by the relation x_{n+1} = (x_{n} + 2)/(x_{n}+3), starting with x_{0} = 3/4. Participants are exploring the behavior of the sequence and its potential limit.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster shares computed values of the sequence and suggests it may be monotone and bounded, prompting questions about how to formally establish convergence. Other participants discuss the implications of assuming convergence and suggest methods to find the limit if convergence is confirmed.

Discussion Status

The discussion is active, with participants providing insights on the necessary conditions for convergence, such as monotonicity and boundedness. There is a focus on the mathematical reasoning behind finding the limit of the sequence, though no consensus has been reached on the convergence itself.

Contextual Notes

Participants note the need to rigorously demonstrate the monotonicity and boundedness of the sequence, as these are critical to establishing convergence. The original poster expresses uncertainty about handling convergence in recursive sequences, indicating a potential gap in foundational understanding.

muzak
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Homework Statement


x_{n+1} = (x_{n} + 2)/(x_{n}+3), x_{0}= 3/4

Homework Equations


The Attempt at a Solution


I've worked out a few of the numbers and got 3/4, 11/15, 41/56, 153/209, ...
It seems to be monotone and bounded below indicating it does converge I think. I need help figuring out what it converges to if it does. I've never really done convergence on a recursive sequence.
 
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Once you know it converges, it is easy to find the limit. Suppose ##x_n\to a## and take the limit of both sides of the recursion to figure out ##a##. Note this argument does not show it converges, only that if it does, the limit is ##a##. You still have to show it is monotone and bounded (if it is).
 
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what is the first thing you think of when you see "n+1"?
 
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If the sequence converges, to x, say, then, taking the limit on both sides, we must have
x= \frac{x+ 2}{x+ 3}
Solve that for x.

Of course, it is not enough to say "It seems to be monotone and bounded below", you must show that it is monotone, you have to show it is.
 
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