Can the first few terms of a convergent infinite series diverge?

In summary, the conversation discusses the convergence of infinite series and whether the initial terms can diverge from the convergence point. It is mentioned that if the series ultimately converges, the specific values of the initial terms do not matter. Additionally, it is noted that the sum of the series can still converge even if the first few terms are relatively large.
  • #1
quasar_4
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I can't remember much from my intro. analysis class anymore.

If you have an infinite series that ultimately converges, can the first few terms diverge (i.e., can they move away from the convergence point)? And if so, how many of these terms can do so?

I'm trying to understand how to "get a feel" for a divergent series. If the first 5000 terms increase, I still can't assume that the rest of the terms will also increase... right?
 
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  • #2
If the series converges, it doesn't matter what any of the terms are. Take 10n/n! for example and look at its graph

http://www2.wolframalpha.com/Calculate/MSP/MSP521197dh1fi067g2gh400004fg666f38h6hb56a?MSPStoreType=image/gif&s=21

It's first few terms are relatively large, yet the sum of the series from 1 to ∞ is e10-1

The first 5000 terms of 5000n/n! will get very large, but the series from 1 to ∞ will still converge to a number: e5000-1

You can add as large a number you want, or a finite number of terms to a convergent series and that doesn't affect its convergence, only the sum of the series.
 
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1. What is a divergent infinite series?

A divergent infinite series is a type of mathematical series where the sum of its terms increases without bound, meaning that it does not have a finite sum. This means that no matter how many terms you add, the sum will continue to grow infinitely.

2. How can you tell if an infinite series is divergent?

One way to determine if an infinite series is divergent is to look at the behavior of its terms. If the terms of the series do not approach zero as the number of terms increases, then the series is most likely divergent. Another way to tell is by using convergence tests, such as the comparison test or the ratio test.

3. Why are divergent infinite series important?

Divergent infinite series are important in mathematics because they can help us understand the concept of infinity and the limitations of our number system. They also have applications in physics and engineering, where infinite series are used to model real-world phenomena.

4. Can a divergent infinite series ever have a sum?

No, a divergent infinite series cannot have a finite sum. By definition, the sum of a divergent infinite series is infinite, meaning that it does not have a specific value. However, in some cases, a divergent infinite series may have a limit, meaning that the sum of its terms approaches a specific value as the number of terms increases.

5. How are divergent infinite series different from convergent infinite series?

The main difference between divergent and convergent infinite series is that convergent series have a finite sum, while divergent series do not. Convergent series also have a specific limit, meaning that the sum of its terms approaches a specific value as the number of terms increases, while divergent series do not have a limit.

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