What's the variable of integration?

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  • #1
SammyS
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Main Question or Discussion Point

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?
 

Answers and Replies

  • #2
CompuChip
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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.
 
  • #3
Ivan Seeking
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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.
 
  • #4
CompuChip
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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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