# Integral ((4x^2)-1)e^(-2x^2)

#### birdhen

I was wondering if anyone could point me in the right direction with this integral.

((4x^2)-1)e^(-2x^2),

I have tried substitution with trig functions, hyperbolic functions, seperating the first part into partial fractions and numerous other methods to no avail. Does anyone who knows have any hints?

Cheers

#### yyat

Try solving this with the http://en.wikipedia.org/wiki/Error_function" [Broken]. This will give a solution in terms of erf(x), a solution in terms of more elementary functions is probably not possible.
I also suspect that the definite integral over the real line is 0.

Last edited by a moderator:

#### birdhen

It is OK I have done it now, I split it in to two parts 4x^2(e-2x^2) and -e(-2x^2) and integrated the first part by parts using u'=4xe(-2x^2) and v=x, and then the integral part of the solution cancelled with the second part ie the sol'n was ;

[-xe(-2x^2)]-int(-e(-2x^2)-int(-e(-2x^2)),

leaving [-xe(-2x^2)] with appropriate limits,

Thanks!

#### HallsofIvy

Science Advisor
Homework Helper
It is OK I have done it now, I split it in to two parts 4x^2(e-2x^2) and -e(-2x^2) and integrated the first part by parts using u'=4xe(-2x^2) and v=x, and then the integral part of the solution cancelled with the second part ie the sol'n was ;

[-xe(-2x^2)]-int(-e(-2x^2)-int(-e(-2x^2)),
No, the last two terms do NOT cancel, they add. This is
$$-xe^{-2x^2}- 2\int e^{-2x^2} dx$$.

leaving [-xe(-2x^2)] with appropriate limits,

Thanks!

#### birdhen

I think wrote it incorrectly, it would be;

(-xe^(-2x^2)) -int(-e^(-2x^2)) -int(e^(-2x^2)),

which then cancels.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving