# What are some convergence tests for series in Real Analysis?

• Necrologist
In summary, the conversation discusses various problems related to series convergence and provides hints and proofs for solving them. The first question asks for a series that diverges by the Root Test but gives no information by the Ratio Test. The second problem proves that if two convergent series of nonnegative numbers are multiplied together, the resulting series will also converge. The third part consists of two subproblems - the first one proving that a series with absolute values that converges can also converge when multiplied by a bounded sequence, and the second one proving that if a series converges, then the limit of its terms is equal to 0.
Necrologist
Hi, I am running short on time, and I am having problems solving the following questions. I do not have any progress on them yet, but I am currently working on it. So any input is very welcome, even if it is just a basis advice on which direction to go with this stuff. Thanks for your time.

1. Find a series Σan which diverges by the Root Test but for which the Ratio Test gives no information.

2. Show that if Σan and Σbn are convergent series of nonnegative numbers, then Σ√anbn (square root of anbn) converges. Hint: Show that √anbn < or = an + bn for all n.

3. a. Prove that if Σ|an| converges and (bn) is a bounded sequence, then Σanbn converges. Hint: Use Theorem 14.4 (a series converges if and only if it satisfies the Cauchy criterion).

b. Observe that Corollary 14.7 (absolutely convergent series are convergent) is a special case of part (a)

obtained by taking bn = 1.4. Let (an) be a sequence with an > 0 for all n ≥ 1, and let Σan be the corresponding series. Prove that if Σan converges, then limn→∞an = 0.

## What is Real Analysis?

Real Analysis is a branch of mathematics that focuses on the study of real numbers and their properties. It deals with concepts such as continuity, limits, derivatives, and integrals.

## What are series in Real Analysis?

In Real Analysis, a series is a sum of terms in a sequence. It is represented by the symbol Σ and can be either finite or infinite. Series play an important role in understanding the convergence and divergence of functions.

## What are some common tests used in Real Analysis?

There are various tests used in Real Analysis to determine the convergence or divergence of a series. Some of the common ones include the Ratio Test, Root Test, Comparison Test, and the Integral Test. These tests can help determine whether a series is convergent or divergent.

## What is the difference between convergence and divergence?

In Real Analysis, convergence refers to a series that approaches a finite limit as the number of terms increases. On the other hand, divergence refers to a series that does not approach a finite limit and instead grows bigger and bigger as the number of terms increases.

## Why is Real Analysis important?

Real Analysis is an essential branch of mathematics that has many applications in various fields, including physics, engineering, and economics. It provides a rigorous foundation for understanding and solving complex problems involving real numbers and functions.

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