How to prove Convergence of this Series

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Homework Help Overview

The discussion revolves around determining the convergence or divergence of the series \(\sum_{i=0}^{\infty} \frac{2^{i} + 3^{i}}{4^{i}+5^{i}}\). Participants are exploring various convergence tests and approaches to analyze the series.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply different convergence tests, including the ratio test and limit comparison, but expresses difficulty in finding a suitable test. Some participants suggest using an asymptotic approach and comparison tests, while others propose hints related to inequalities.

Discussion Status

The discussion is active, with participants providing hints and suggestions for potential approaches. There is a recognition of the challenges faced in applying certain tests, and some participants seem to find clarity in the discussion.

Contextual Notes

Participants are working within the constraints of homework rules, which may limit the types of solutions or methods they can explore. The original poster mentions using Mathematica for initial analysis, indicating reliance on computational tools for verification.

Euler2718
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Homework Statement



Use any appropriate test to determine the convergence or divergence of the following series:

[tex]\sum_{i=0}^{\infty} \frac{2^{i} + 3^{i}}{4^{i}+5^{i}}[/tex]

Homework Equations

The Attempt at a Solution



I've run it through mathematica and it told me it's convergent. However, I can't seem to find the right test to use. Ratio test / Limit comparison doesn't seem to work as nothing cancels, I can't find a test series for direct comparison, and root test wouldn't work? Have I over looked anything?
 
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You can start with an asymptotic approach ##\sum_{i=0}^{\infty}\frac{2^{i}+3^{i}}{4^{i}+5^{i}}\sim \sum_{i=0}^{\infty}\frac{3^{i}}{5^{i}}##
 
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Morgan Chafe said:

Homework Statement



Use any appropriate test to determine the convergence or divergence of the following series:

[tex]\sum_{i=0}^{\infty} \frac{2^{i} + 3^{i}}{4^{i}+5^{i}}[/tex]

Homework Equations

The Attempt at a Solution



I've run it through mathematica and it told me it's convergent. However, I can't seem to find the right test to use. Ratio test / Limit comparison doesn't seem to work as nothing cancels, I can't find a test series for direct comparison, and root test wouldn't work? Have I over looked anything?
Try comparison test.
Hint: if 0<a<b and 0<c, 0<d, then ##\frac{a+b}{c+d}\leq \frac{2b}{d}##
 
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How about : ## 0<a<b<c<d ## then ##\frac {a+b}{c+d} ##?
 
Ssnow said:
You can start with an asymptotic approach ##\sum_{i=0}^{\infty}\frac{2^{i}+3^{i}}{4^{i}+5^{i}}\sim \sum_{i=0}^{\infty}\frac{3^{i}}{5^{i}}##
Samy_A said:
Try comparison test.
Hint: if 0<a<b and 0<c, 0<d, then ##\frac{a+b}{c+d}\leq \frac{2b}{d}##

Alright I think I got it now, thanks.
 

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