How to prove Convergence of this Series

In summary, the conversation discusses using an appropriate test to determine the convergence or divergence of the series. The attempt at a solution involves using an asymptotic approach and the comparison test to determine that the series is convergent. The conversation also provides hints and clarifications for using the comparison test.
  • #1
Euler2718
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3

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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  • #2
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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  • #3
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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  • #4
How about : ## 0<a<b<c<d ## then ##\frac {a+b}{c+d} ##?
 
  • #5
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.
 

What is the definition of convergence of a series?

Convergence of a series refers to the property of a mathematical series where the terms of the series approach a finite value as the number of terms increases. In simpler terms, it means that the sum of the terms in the series approaches a specific value as more terms are added.

How do you prove convergence of a series?

To prove convergence of a series, you can use various methods such as the comparison test, ratio test, root test, and integral test. These methods involve comparing the given series to a known series or using mathematical operations to determine the behavior of the series as the number of terms increases.

What is the role of the limit in proving convergence of a series?

The limit plays a crucial role in proving convergence of a series. In order for a series to converge, the limit of its terms must approach a finite value as the number of terms increases. This is the key concept behind all convergence tests and is essential in determining the behavior of a series.

Can a series converge if its terms do not approach zero?

No, a series cannot converge if its terms do not approach zero. This is because the limit of the series' terms must approach zero for the series to converge. If the terms do not approach zero, it means that the series is either divergent or oscillatory, and therefore cannot converge.

What are some real-world applications of proving convergence of a series?

Proving convergence of a series is essential in many scientific fields, including physics, engineering, and economics. It is used to analyze the behavior of systems and processes that involve a changing number of terms, such as in power series, Fourier series, and Taylor series. In economics, the concept of convergence is used to study economic growth and the behavior of financial markets.

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