Estimating the sum of an alternating series by the 40th partial sum

Click For Summary

Homework Help Overview

The discussion revolves around approximating the sum of the alternating series \(\sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n^4}\) using the 40th partial sum and estimating the associated error. Participants are exploring methods to compute this partial sum and understand the underlying concepts.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the method of bounding the error using the absolute value of the next term in the series. There are questions about how to compute the 40th partial sum and whether a specific formula is needed. Some express uncertainty about the calculation process and the use of computational tools.

Discussion Status

The discussion is ongoing, with participants sharing insights about the relationship between the series and the Riemann zeta function. Some suggest that computational methods may be necessary for calculating the partial sums, while others seek clarification on the calculation process itself.

Contextual Notes

Participants note that the problem is not for an exam or assignment but is drawn from a textbook example, which may influence their approach to understanding the calculation of the series sum.

donald1403
Messages
16
Reaction score
0

Homework Statement


Approximate the sum of the alternating series [tex]\sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n^4}[/tex] by the 40th partial sum and estimate the error in this approximation.


I know how to calculute the sum of the alternating series by 4th or 5th partial sum. I don't think this problem wants me to calculate till 40th partial sum.

How can I calculate like 40th partial sum or 100th partial sum?
 
Physics news on Phys.org
You can bound the error of the 40th partial sum by looking at the absolute value of the 41st term in the series. It's an alternating series.
 
the absolute value of the 41st term would be 3.54 x 10^(-7) . but it would only mean that the sum of the series will be within 3.54 x 10^(-7). but how can i calculate the sum of the series. this is not for exam or assignment. this is just an example in the textbook. the answer is

S = S40 = 0.9470326439 but they just wrote down the answer but didn't really explain how they get that number? what formula should i use to calculate the sum of the series?
 
Good point. The infinite sum is related to the Riemann zeta function. It's (7/8)*zeta(4). http://mathworld.wolfram.com/RiemannZetaFunction.html That's all tons of fun and stuff, but I don't know any shortcut formula to get the partial sums. I think they maybe did use a computer to compute the partial sum. You can write a short program (preferably) or use a spreadsheet approach if you're desperate.
 
thanks again, Dick. I just need to make sure they use computer or calculator to calculate the sum. I sure can calculate by hand for few terms but jz wondering if there is any way to calculate. I guess I just have to depend on calculator. anyway, thanks again!
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
1
Views
1K
  • · Replies 12 ·
Replies
12
Views
3K
Replies
2
Views
5K
Replies
14
Views
2K
  • · Replies 17 ·
Replies
17
Views
5K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K