# Integral problem

## Homework Statement

http://www4.0zz0.com/2007/02/16/20/74624071.bmp [Broken]

## Homework Equations

Can any body help me with this integral problem???Please.

## The Attempt at a Solution

Is the only solution by the "douple integration" method ???

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NateTG
Homework Helper
What have you tried?

Calc I or Calc II? Are you sure you wrote that problem down correctly?

(edit: have you heard of the imaginary error function? Either that, or I'm completely blanking out on this one.)

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I'm really sorry. I've written the problem down uncorrectly This is the right one:_
http://www4.0zz0.com/2007/02/16/21/95988123.bmp [Broken]

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Hootenanny
Staff Emeritus
Gold Member
Try rewriting the problem;

$$\int e^{-x^2}\cdot e^{-\frac{1}{x^2}} dx$$

I tried this step,but I couldn't continue.

Maybe we need "douple integration" here.

cheat with this site:

http://integrals.wolfram.com/index.jsp

enter your function as follows: Exp[-x^2-1/x^2]

You will see that it is not an easy one.

However, I guess that for a definite integral {-Inf,+Inf} it could be easier.
Are you sure you want the indefinite integral?

If yes, you can still try to figure out out to get by hand the result mathematica will show you.

The result is:

Integrate[Exp[-x^2 - 1/x^2], x] ==
(Sqrt[Pi]*((1 + Erf[-x^(-1) + x])/E^2 + E^2*(-1 + Erf[x^(-1) + x])))/4

Thank you very much for the wonderful site,and for replying.

I've tried it,and I saw the result. But as you said,I want to figure out how to get by hand the result.

I still need help.

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I want to figure out how to get by hand the result

That's where cheating becomes really an art.
Try calculating the derivate of the result and write the calculation in reverse order.

In this process you may have some good idea.

Another method is to look in the Mathematica package how it does that.
It is very difficult to read, but it is easy to guess the ingredients.
Probably a standard form we be used and some integral table results (not many since erf is an easy function).
But you need Mathematica ... and that's very expensive

Great ideas,especially that one about cheating:rofl: I will try this one,because I can't use Mathematica package right now.
And we will see 