Example of a Telescoping Series

Oct 13, 2025 by wbrum.org 34 views

Introduction

A telescoping series is a type of infinite series where the terms of the series cancel out, leaving only a few terms. This type of series is called "telescoping" because the terms of the series "telescope" or collapse into a smaller number of terms. In this article, we will discuss how to find a formula for the nth term of the sequence of partial sums of a telescoping series and evaluate the limit of the sequence of partial sums to obtain the value of the series.

What is a Telescoping Series?

A telescoping series is an infinite series of the form:

\sum_{n=1}^{\infty} a_n = a_1 + a_2 + a_3 + \ldots

where the terms of the series are such that:

a_{n+1} = a_n - b_n

for some sequence of numbers $b_n$ . This means that each term of the series is equal to the previous term minus some number $b_n$ .

Example of a Telescoping Series

Consider the series:

\sum_{n=1}^{\infty} \frac{1}{n(n+1)}

This series is a telescoping series because the terms of the series can be written as:

\frac{1}{n(n+1)} = \frac{1}{n} - \frac{1}{n+1}

Finding the nth Term of the Sequence of Partial Sums

To find the nth term of the sequence of partial sums, we need to find the sum of the first n terms of the series. Let's call this sum $S_n$ . Then, we can write:

S_n = \sum_{k=1}^n a_k

Using the formula for the telescoping series, we can write:

S_n = \sum_{k=1}^n \left( \frac{1}{k} - \frac{1}{k+1} \right)

Evaluating the Limit of the Sequence of Partial Sums

To evaluate the limit of the sequence of partial sums, we need to find the limit of $S_n$ as $n$ approaches infinity. Let's call this limit $S$ . Then, we can write:

S = \lim_{n \to \infty} S_n

Using the formula for the telescoping series, we can write:

S = \lim_{n \to \infty} \sum_{k=1}^n \left( \frac{1}{k} - \frac{1}{k+1} \right)

Simplifying the Expression for S

To simplify the expression for $S$ , we can use the fact that the terms of the series cancel out. Specifically, we can write:

S = \lim_{n \to \infty} \left( \frac{1}{1} - \frac{1}{2} + \frac{1}{2} - \frac{1}{3} + \frac{1}{3} - \frac{1}{4} + \ldots + \frac{1}{n} - \frac{1}{n+1} \right)

Cancelling Out the Terms

The terms of the series cancel out, leaving only the first and last terms. Specifically, we can write:

S = \lim_{n \to \infty} \left( \frac{1}{1} - \frac{1}{n+1} \right)

Evaluating the Limit

To evaluate the limit, we can use the fact that the limit of a constant is the constant itself. Specifically, we can write:

S = \frac{1}{1} - \lim_{n \to \infty} \frac{1}{n+1}

Simplifying the Expression for S

To simplify the expression for $S$ , we can use the fact that the limit of a constant is the constant itself. Specifically, we can write:

S = 1 - 0

The Final Answer

The final answer is:

S = 1

Conclusion

In this article, we discussed how to find a formula for the nth term of the sequence of partial sums of a telescoping series and evaluate the limit of the sequence of partial sums to obtain the value of the series. We used the example of the series $\sum_{n=1}^{\infty} \frac{1}{n(n+1)}$ to illustrate the process. We showed that the series is a telescoping series and found the formula for the nth term of the sequence of partial sums. We then evaluated the limit of the sequence of partial sums to obtain the value of the series, which is 1.

Future Work

In the future, we can use the techniques developed in this article to evaluate other telescoping series. We can also use the techniques to evaluate other types of series, such as convergent and divergent series.

References

[1] "Telescoping Series" by MathWorld
[2] "Infinite Series" by Wolfram MathWorld
[3] "Telescoping Series" by Khan Academy

Glossary

Telescoping Series: A type of infinite series where the terms of the series cancel out, leaving only a few terms.
Partial Sums: The sum of the first n terms of a series.
Limit: The value that a sequence approaches as the number of terms increases without bound.
Convergent Series: A series that converges to a finite limit.
Divergent Series: A series that diverges to infinity.

Introduction

In our previous article, we discussed how to find a formula for the nth term of the sequence of partial sums of a telescoping series and evaluate the limit of the sequence of partial sums to obtain the value of the series. In this article, we will answer some frequently asked questions about telescoping series.

Q: What is a telescoping series?

A: A telescoping series is a type of infinite series where the terms of the series cancel out, leaving only a few terms. This type of series is called "telescoping" because the terms of the series "telescope" or collapse into a smaller number of terms.

Q: How do I know if a series is a telescoping series?

A: To determine if a series is a telescoping series, you need to check if the terms of the series can be written in the form:

a_{n+1} = a_n - b_n

for some sequence of numbers $b_n$ . If the terms of the series can be written in this form, then the series is a telescoping series.

Q: How do I find the nth term of the sequence of partial sums of a telescoping series?

A: To find the nth term of the sequence of partial sums of a telescoping series, you need to find the sum of the first n terms of the series. Let's call this sum $S_n$ . Then, you can write:

S_n = \sum_{k=1}^n a_k

Using the formula for the telescoping series, you can write:

S_n = \sum_{k=1}^n \left( \frac{1}{k} - \frac{1}{k+1} \right)

Q: How do I evaluate the limit of the sequence of partial sums of a telescoping series?

A: To evaluate the limit of the sequence of partial sums of a telescoping series, you need to find the limit of $S_n$ as $n$ approaches infinity. Let's call this limit $S$ . Then, you can write:

S = \lim_{n \to \infty} S_n

Using the formula for the telescoping series, you can write:

S = \lim_{n \to \infty} \sum_{k=1}^n \left( \frac{1}{k} - \frac{1}{k+1} \right)

Q: What is the value of the series?

A: The value of the series is the limit of the sequence of partial sums, which is $S$ .

Q: Can I use the techniques developed in this article to evaluate other types of series?

A: Yes, you can use the techniques developed in this article to evaluate other types of series, such as convergent and divergent series.

Q: What are some common examples of telescoping series?

A: Some common examples of telescoping series include:

The series $\sum_{n=1}^{\infty} \frac{1}{n(n+1)}$
The series $\sum_{n=1}^{\infty} \frac{1}{n^2}$
The series $\sum_{n=1}^{\infty} \frac{1}{n^3}$

Q: How do I determine if a series is convergent or divergent?

A: To determine if a series is convergent or divergent, you need to evaluate the limit of the sequence of partial sums. If the limit exists, then the series is convergent. If the limit does not exist, then the series is divergent.

Q: What are some common mistakes to avoid when working with telescoping series?

A: Some common mistakes to avoid when working with telescoping series include:

Not recognizing that a series is a telescoping series
Not using the correct formula for the nth term of the sequence of partial sums
Not evaluating the limit of the sequence of partial sums correctly

Conclusion

In this article, we answered some frequently asked questions about telescoping series. We discussed how to determine if a series is a telescoping series, how to find the nth term of the sequence of partial sums, and how to evaluate the limit of the sequence of partial sums. We also discussed some common examples of telescoping series and how to determine if a series is convergent or divergent. Finally, we discussed some common mistakes to avoid when working with telescoping series.

References

[1] "Telescoping Series" by MathWorld
[2] "Infinite Series" by Wolfram MathWorld
[3] "Telescoping Series" by Khan Academy

Glossary

Telescoping Series: A type of infinite series where the terms of the series cancel out, leaving only a few terms.
Partial Sums: The sum of the first n terms of a series.
Limit: The value that a sequence approaches as the number of terms increases without bound.
Convergent Series: A series that converges to a finite limit.
Divergent Series: A series that diverges to infinity.