Integration and taylor expansion

[casanova2528]

can anybody help me with this integration?

Integral of e to the -2x times x squared dx

it expands to 1/4, but I'm not sure how to start.

 

[Hootenanny]

can anybody help me with this integration?

Integral of e to the -2x times x squared dx

it expands to 1/4, but I'm not sure how to start.

Hey casanova, welcome to PF!

You don't really need a Taylor expansion here, how about trying a substitution?

 

[casanova2528]

I have tried substitution

I've already tried substitution.

argh!

i've tried u = e ^ -2x

I've also tried u = x squared.

it doesn't work!

HELP!

 

[Ed Aboud]

Integrate by parts and it works.

 

[casanova2528]

start me off

with what do I start?

 

[rock.freak667]

with what do I start?

you start by integrating

\int xe^{-2x}dx

by parts.

 

[csprof2000]

You integrate by parts. Start with x squared. You get

u = x^2
du = 2x dx

dv = e^-2x dx
v = -1/2 e^-2x

Give it a shot from there.

 

[casanova2528]

thanks

i get it now...just needed a refresher...thanks a lot!