Power Series Representation of a Function

Oct 13, 2025 by wbrum.org 106 views

Introduction

In calculus, the power series representation of a function is a way to express the function as an infinite sum of terms, each of which is a power of the variable. The power series representation of a function is useful for solving problems involving the function, such as finding the antiderivative of the function. In this article, we will discuss how to determine a power series representation for the antiderivative of a function with a given power series representation.

Power Series Representation of a Function

A power series representation of a function $f(x)$ is an infinite sum of terms, each of which is a power of the variable $x$ . The power series representation of a function is written in the form:

f(x) = \sum_{n=0}^{\infty} a_n x^n

where $a_n$ are the coefficients of the power series. The radius of convergence of the power series is the distance from the center of the power series to the nearest point where the power series diverges.

Power Series Representation of the Function $f(x)$

The power series representation of the function $f(x)$ is given by:

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

The radius of convergence of the power series is $R=1$ . This means that the power series converges for all values of $x$ such that $|x| < 1$ .

Determining a Power Series Representation for the Antiderivative

To determine a power series representation for the antiderivative of the function $f(x)$ , we need to integrate the power series representation of the function. The antiderivative of the function $f(x)$ is denoted by $F(x)$ and is given by:

F(x) = \int f(x) dx

To integrate the power series representation of the function, we can use the following formula:

\int \sum_{n=1}^{\infty} a_n x^n dx = \sum_{n=1}^{\infty} \frac{a_n}{n+1} x^{n+1} + C

where $C$ is the constant of integration.

Integrating the Power Series Representation of the Function $f(x)$

To integrate the power series representation of the function $f(x)$ , we can use the formula above. We have:

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

Integrating the power series representation of the function, we get:

F(x) = \int f(x) dx = \sum_{n=1}^{\infty} \frac{1}{n(n+1)} x^{n+1} + C

Simplifying the expression, we get:

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

Simplifying the Power Series Representation of the Antiderivative

To simplify the power series representation of the antiderivative, we can use the following formula:

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

Using this formula, we can simplify the power series representation of the antiderivative as follows:

F(x) = \sum_{n=1}^{\infty} \frac{x^{n+1}}{n} - \sum_{n=1}^{\infty} \frac{x^{n+1}}{n+1} + C

Simplifying further, we get:

F(x) = x \sum_{n=1}^{\infty} \frac{x^n}{n} - \sum_{n=1}^{\infty} \frac{x^{n+1}}{n+1} + C

Conclusion

In this article, we discussed how to determine a power series representation for the antiderivative of a function with a given power series representation. We used the formula for integrating a power series representation of a function to find the power series representation of the antiderivative. We also simplified the power series representation of the antiderivative using a formula for simplifying a power series representation of a function.

References

[1] Calculus, by Michael Spivak
[2] Power Series, by Wolfram MathWorld
[3] Antiderivative, by Wolfram MathWorld

Introduction

In our previous article, we discussed how to determine a power series representation for the antiderivative of a function with a given power series representation. In this article, we will answer some frequently asked questions about power series representation of a function and its antiderivative.

Q&A

Q: What is a power series representation of a function?

A: A power series representation of a function is an infinite sum of terms, each of which is a power of the variable. The power series representation of a function is written in the form:

f(x) = \sum_{n=0}^{\infty} a_n x^n

where $a_n$ are the coefficients of the power series.

Q: What is the radius of convergence of a power series representation of a function?

A: The radius of convergence of a power series representation of a function is the distance from the center of the power series to the nearest point where the power series diverges.

Q: How do I determine a power series representation for the antiderivative of a function?

A: To determine a power series representation for the antiderivative of a function, you need to integrate the power series representation of the function. The antiderivative of the function $f(x)$ is denoted by $F(x)$ and is given by:

F(x) = \int f(x) dx

To integrate the power series representation of the function, you can use the following formula:

\int \sum_{n=1}^{\infty} a_n x^n dx = \sum_{n=1}^{\infty} \frac{a_n}{n+1} x^{n+1} + C

where $C$ is the constant of integration.

Q: How do I simplify a power series representation of the antiderivative?

A: To simplify a power series representation of the antiderivative, you can use the following formula:

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

Using this formula, you can simplify the power series representation of the antiderivative as follows:

F(x) = x \sum_{n=1}^{\infty} \frac{x^n}{n} - \sum_{n=1}^{\infty} \frac{x^{n+1}}{n+1} + C

Q: What are some common applications of power series representation of a function and its antiderivative?

A: Power series representation of a function and its antiderivative have many common applications in mathematics and physics. Some common applications include:

Solving differential equations
Finding the area under a curve
Finding the volume of a solid
Finding the work done by a force

Q: How do I use power series representation of a function and its antiderivative in real-world problems?

A: To use power series representation of a function and its antiderivative in real-world problems, you need to apply the concepts and formulas discussed in this article to the specific problem you are trying to solve. For example, if you are trying to find the area under a curve, you can use the power series representation of the function to find the antiderivative and then integrate it to find the area.

Conclusion

In this article, we answered some frequently asked questions about power series representation of a function and its antiderivative. We discussed the power series representation of a function, the radius of convergence of a power series representation of a function, and how to determine a power series representation for the antiderivative of a function. We also discussed how to simplify a power series representation of the antiderivative and some common applications of power series representation of a function and its antiderivative.

References

[1] Calculus, by Michael Spivak
[2] Power Series, by Wolfram MathWorld
[3] Antiderivative, by Wolfram MathWorld