# Introduction to Power Series and The Convergence Theorem | Summary and Q&A

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May 24, 2020
by
The Math Sorcerer
Introduction to Power Series and The Convergence Theorem

## TL;DR

Power series are infinite sums that are centered around a specific value, and the convergence theorem identifies three possible outcomes for power series: convergence only at the center, convergence within a specific interval, or convergence everywhere.

## Key Insights

• ✊ A power series is an infinite sum centered around a specific value.
• ✊ The convergence theorem for power series provides three possible outcomes: convergence only at the center, convergence within an interval, or convergence everywhere.
• ✊ The radius of convergence determines the size of the interval or disk where the power series converges.
• ✊ Complex numbers can also be used in power series and have their own interval of convergence.
• 💁 The convergence theorem does not provide information about convergence at the endpoints of the interval.
• 🥳 The ratio test is commonly used to determine the interval of convergence for a power series.
• ✊ Finding the interval and radius of convergence is essential in analyzing the behavior of power series.

## Transcript

in this video we're going to introduce the notion of power series and then talk about something called the convergence theorem for power series so first this is a power series so if you have an infinite sum that starts say at zero it goes to infinity and you have a sub n times x minus c to the n this is called a power series centered at c so this i... Read More

### Q: What is a power series and how is it defined?

A power series is an infinite sum of the form a.sub.n * (x - c)^n, where c is the center of the series and a.sub.n are the coefficients.

### Q: What happens when the center of the power series is zero?

When the center is zero, the power series simplifies to a.sub.n * x^n, which is a power series centered at zero.

### Q: What does the convergence theorem for power series state?

The convergence theorem for power series states that a power series can have three possible outcomes: convergence only at the center, convergence within a specific interval, or convergence everywhere.

### Q: How can the convergence theorem be applied to complex numbers?

The convergence theorem applies to complex numbers as well, where the interval of convergence becomes an open disk centered around the complex number c.

## Summary & Key Takeaways

• Power series are defined as infinite sums of the form a.sub.n * (x - c)^n, where c is the center of the series and a.sub.n are the coefficients.

• When the center is zero, the power series simplifies to a.sub.n * x^n, which is a power series centered at zero.

• The convergence theorem for power series states that a power series can only have one of three outcomes: convergence only at the center, convergence within a specific interval, or convergence everywhere.