# Error in Textbook Series: Who is Right?

• malawi_glenn
In summary, the conversation revolved around an error found in a textbook regarding the convergence of a geometric series. The textbook stated that the series converges for |z| < 1/2, but the individual checking the series found it to converge for |z| < 1/sqrt(2). They asked if their calculations were correct and if there was an error in the textbook. The conversation then turned to discussing the methods used to prove convergence and the difference between necessary and sufficient conditions. Ultimately, the conversation concluded with the understanding that mistakes in textbooks are common and the importance of treating others with respect.

#### malawi_glenn

Homework Helper
Gold Member
Hi i found this "error" in my textbook in series.

https://www.physicsforums.com/attachment.php?attachmentid=9420&stc=1&d=1173538014

This is a geometric one, it converges for |z|< 1/rot(2) when i calculate this, but the textbook claims that |z|<1/2

I also checked different values on z and i get a finite value even when z is 0,7
[ 0,5< 0,7 < 1/rot(2) ]

Who is right?

#### Attachments

• serie2.JPG
5.8 KB · Views: 601
An error in a textbook? I've never seen such a thing before!

Why do you think a book is constantly revised with newer editions?

How did you evaluate an infinite sum in a finite time?

If the result is true when $$|z| < 1/\sqrt 2$$, then it is true when $$|z| < 1/2$$.

So what's the error?

Yes of course i know that books don't have right all the time, but science i didn't find that in the errata, i wanted to ask others to see if i was right or not.. why are you all so upset?!? Why can't you just confirm my discovery so that i can report this to the author?

And yes, of course |z| < 1/2 is ONE solution, but the author is giving the COMPLETE solution in all other places in the book, so you must be consistent...

And its not that hard to check if an geometric series is convergent or divergent.. just take n=156 on your calculator than you take 157 etc, and you see if the value is getting close to 1/(1-x) ... (if x is the argument in your geometric series)... The value of a geometric serie is less than unity if the serie converges as n goes to infinity..

So you put a few terms into a calculator and decided that was the behaviour for infinitely many terms? That isn't how you prove things.

It does look like a mistake, by the way.

matt grime said:
So you put a few terms into a calculator and decided that was the behaviour for infinitely many terms? That isn't how you prove things.

It does look like a mistake, by the way.

I never stated that i PROOVED, i checked.. and as i said, for a geometric serie it is a trivial thing to see..

Yea matt I do that sometimes as well, it doesn't prove anything at all, but sometimes its obvious what its converging to, can give you a tiny prod in the right direction.

If you check it, then you demonstrate it to be true, i.e. you prove it. Numerical things like this merely suggest, they do not verify.

matt grime said:
If you check it, then you demonstrate it to be true, i.e. you prove it. Numerical things like this merely suggest, they do not verify.

No i checked if the sum SEEMED to reach a finite value for different |z|, THATS WHY i asked if my assumptions were correct.

Why can't you just answer my questions in the first place? Why must everybody be so besserwisser? "omg an error in textbook, no way", those kind of things.. And "well if it is true for |z|<1/rot2 , than it is also true for |z|<1/2", are you all in a bad mood or so? Why can't you be helpful?!

We're trying to be helpful, please note these are people who are not getting paid to answer your questions! These people are very knowledgeable people who could better use their time! If you think they are being pedantic, hack it, your getting free advice from smart people!

Gib Z said:
We're trying to be helpful, please note these are people who are not getting paid to answer your questions! These people are very knowledgeable people who could better use their time! If you think they are being pedantic, hack it, your getting free advice from smart people!

Treat your neighbour as you self want to be treated..

malawi_glenn said:
No i checked if the sum SEEMED to reach a finite value for different |z|, THATS WHY i asked if my assumptions were correct.

you have been answered on this topic.

"omg an error in textbook, no way",

it's irony. mistakes in textbooks are very frequent, and almost not worth pointing out.

And "well if it is true for |z|<1/rot2 , than it is also true for |z|<1/2", are you all in a bad mood or so? Why can't you be helpful?!

this was pointing out that it wasn't clear if you were asking for a sufficient condition or a necessary and sufficient condition.

If you had said that the book asserted the radius of convergence was something, then that would be different. What you wrote is, if as litereally appears in the book, perfectly correct. That sum does converge for |z|<1/2. That is not the radius of convergence, but that is strictly a different matter from what you asked.

## 1. What is the error in the textbook series?

The error in the textbook series is a mistake or inaccuracy in the information presented in the series.

## 2. Who is responsible for the error in the textbook series?

It is important to determine who is responsible for the error in the textbook series in order to address the issue and prevent it from happening again. This could include the author, editor, publisher, or other individuals involved in creating the series.

## 3. How was the error in the textbook series discovered?

The error in the textbook series may have been discovered through various means, such as through a review process, by a reader or educator, or through further research and analysis.

## 4. What impact does the error in the textbook series have?

The impact of the error in the textbook series can vary depending on the nature of the error and the subject matter. It could potentially mislead readers, cause confusion, or affect the accuracy of the information being taught.

## 5. How can the error in the textbook series be corrected?

The error in the textbook series can be corrected by identifying the mistake and providing a correction or update to the information. This could involve issuing a revised edition, creating an errata page, or providing supplemental materials.

• General Math
Replies
20
Views
1K
• Calculus and Beyond Homework Help
Replies
2
Views
1K
• Science and Math Textbooks
Replies
19
Views
610
Replies
3
Views
740
• Linear and Abstract Algebra
Replies
8
Views
585
• General Math
Replies
5
Views
1K
• General Math
Replies
1
Views
917
• General Math
Replies
5
Views
2K
• Calculus and Beyond Homework Help
Replies
3
Views
266
• General Math
Replies
9
Views
1K