What Are the Limits of {xn} and {yn} in the Given Sequence?

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Discussion Overview

The discussion revolves around the limits of two sequences, {xn} and {yn}, defined recursively based on initial values x0 and y0, where x0 > y0 > 0. Participants explore the conditions under which these sequences converge and the proposed limits.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the limits of the sequences are both equal to sqrt(x0y0), questioning the validity of this conclusion.
  • Another participant challenges the initial formulation of the problem, indicating that the sequences diverge under certain conditions.
  • A later post corrects the problem statement and reiterates the proposed limits, maintaining the same conclusion.
  • Participants discuss the behavior of the sequences, with one suggesting that xn is decreasing and yn is increasing, and proposing to show that xn has a lower bound while yn has an upper bound.
  • There is a request for clarification on the assertion that convergence is a well-known fact, indicating a desire for deeper understanding.

Areas of Agreement / Disagreement

Participants express differing views on the initial problem formulation and the proposed limits. While some support the idea of convergence to sqrt(x0y0), others contest the validity of the initial conditions and the conclusions drawn.

Contextual Notes

The discussion includes assumptions about the behavior of the sequences and their convergence properties, which have not been fully established or agreed upon by all participants. The implications of the initial values on the sequences' behavior remain unresolved.

Who May Find This Useful

This discussion may be of interest to those studying recursive sequences, convergence criteria, or related mathematical concepts in analysis.

huey910
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Given x0 and y0 such that x0 > y0 > 0. Define, for n = 0,1,2,,
xn+1 =xn +yn , yn+1 = 2xnyn .Find the limits of {xn} and {yn}.

why is the answer lim{xn} = lim{yn} = sqrt(x0y0)?
 
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The problem as stated is wrong (e.g. x0 = 2, y0 =1. they just keep getting bigger).
 
Oh! Sorry, I transcribed the question erroneously. It should be:

Given x0 and y0 such that x0 > y0 > 0. Define, for n = 0,1,2,,
xn+1 =(xn +yn)/2 , yn+1 = 2xnyn/(xn + yn) .Find the limits of {xn} and {yn}.

why is the answer lim{xn} = lim{yn} = sqrt(x0y0)?
 
1) Show that x_n is decreasing, and y_n is increasing.
2) Show that x_n has a lower bound, and y_n has an upper bound.

Hint: Show that x_n < y_n by induction, and then that x_n+1 < x_n, and y_n+1 > y_n.

Do you know why they must converge in this case? It is a well known fact.

3) Find the limits by using the equations.
 
It is a well-known fact? Please expand on it and enlighten me! Thank you for the hints though!
 

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