Proving that the sum of (u^x)/x from 0 to infinity = e^u

  • Context: Graduate 
  • Thread starter Thread starter CraigH
  • Start date Start date
  • Tags Tags
    Infinity Sum
Click For Summary

Discussion Overview

The discussion revolves around the derivation of the formula for the sum of the series \(\sum^{∞}_{0}\frac{u^{x}}{x!} = e^{u}\). Participants explore the connection between this series and the definition of the exponential function, as well as its relation to the MacLaurin series expansion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant requests a derivation of the formula for the sum of \(\frac{u^{x}}{x!}\) from 0 to infinity.
  • Another participant suggests that this formula is essentially the definition of \(e^u\) and hints at verification through differentiation.
  • A participant inquires about the MacLaurin series expansion and its relevance to the discussion.
  • A later reply confirms that the MacLaurin series for \(e^x\) provides the answer sought, indicating its use in a proof for a different equation.

Areas of Agreement / Disagreement

Participants appear to agree on the connection between the series and the definition of \(e^u\), but the discussion does not resolve the derivation process itself, leaving some aspects open for further exploration.

Contextual Notes

The discussion references the MacLaurin series without detailing its derivation or assumptions, and the connection to the proof for a different equation remains unspecified.

Physics news on Phys.org
Hi CraigH! :smile:

Isn't that the definition of eu ?

(and you can check it by working out euev, or by differentiating it :wink:)
 
Do you know about the MacLaurin series expansion ? What is it for ex ?
 
Ah yes, I've just looked up the MacLaurin series for e^x in my data book, its give me the answer i was hoping for. I needed to know as part of a proof for a different equation.

So in my exam just saying:

"From the MacLaurin series:
The sum of (u^x)/x! from 0 to infinity = e^u"

Should be enough then.

Thank you for answering.
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
7K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 15 ·
Replies
15
Views
4K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
12K