What's the variable of integration?

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Discussion Overview

The discussion revolves around the clarity and ambiguity of notation in integral calculus, specifically regarding the variable of integration in expressions like \(\int xe^{-ax}\). Participants explore the implications of not specifying the variable and how it can lead to confusion in mathematical communication.

Discussion Character

  • Conceptual clarification, Debate/contested, Meta-discussion

Main Points Raised

  • One participant questions the clarity of the variable of integration in the expression \(\int xe^{-ax}\), suggesting it could be interpreted with different variables.
  • Another participant acknowledges that while the convention typically implies \(x\) as the variable and \(a\) as a constant, the notation is not entirely unambiguous and may require clarification.
  • A third participant shares a humorous anecdote about a professor who was cautious about using a dummy variable for integration, highlighting the potential for scrutiny in mathematical notation.
  • One participant jokingly suggests that in a homework context, one might submit an integral without explicitly stating the variable, emphasizing the informal nature of such discussions.

Areas of Agreement / Disagreement

Participants generally agree that the notation can be ambiguous, but there is no consensus on how critical this ambiguity is in practice. Some view it as a minor issue, while others believe it warrants attention.

Contextual Notes

The discussion does not resolve the implications of using ambiguous notation, nor does it clarify the assumptions underlying the use of variables in integration.

SammyS
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What's the variable of integration?

I keep seeing posts like this:
Help me do this integral

[tex] \int xe^{-ax}[/tex]

Shouldn't we all ask, right off the bat, "What's the variable of integration?"

Probably what was meant was:

[tex]\int xe^{-ax}\, dx \,.[/tex]

But maybe the problem actually was:

[tex]\int xe^{-ax}\, da \,.[/tex]

Does this bother any of you?
 
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Although it is rather clear what was meant (by the convention of using x for a variable and a for a constant) I agree that the notation is not completely unambiguous.
Depending on the context, it would be important or nit-picky (is that a word?) to point this out to the one who gave you that expression.
 


I am reminded of an old physics professor who, when using a dummy variable x for integration of the real variable x, would sheepishly look around the room checking for any math police.
 


And if you are really brave, and this were a homework problem, you might just write down
[tex]\int x e^{ax} = e^{ax} + c[/tex]
(don't forget the + c :-P) and hand it in like that :)
 

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