# What's the variable of integration?

Staff Emeritus
Homework Helper
Gold Member

## Main Question or Discussion Point

What's the variable of integration???

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

$$\int xe^{-ax}$$
Shouldn't we all ask, right off the bat, "What's the variable of integration?"

Probably what was meant was:

$$\int xe^{-ax}\, dx \,.$$

But maybe the problem actually was:

$$\int xe^{-ax}\, da \,.$$

Does this bother any of you?

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CompuChip
Homework Helper

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.

Ivan Seeking
Staff Emeritus
Gold Member

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.

CompuChip
$$\int x e^{ax} = e^{ax} + c$$