# Need help solving simple integral

• Feb 29th 2012, 03:06 AM
downthesun01
Need help solving simple integral
Wolfram Alpha gives an answer of $\frac{1}{2}$, but it doesn't give the steps. Can someone walk me through the problem or a similar problem? I believe I need to use integration by parts but I keep getting stuck.

Thanks

$\int_{0}^{\infty}\frac{3x}{(1+x)^{4}}dx$
• Feb 29th 2012, 03:16 AM
skeeter
Re: Need help solving simple integral
Quote:

Originally Posted by downthesun01
Wolfram Alpha gives an answer of $\frac{1}{2}$, but it doesn't give the steps. Can someone walk me through the problem or a similar problem? I believe I need to use integration by parts but I keep getting stuck.

Thanks

$\int_{0}^{\infty}\frac{3x}{(1+x)^{4}}dx$

try the substitution $u = x+1$
• Feb 29th 2012, 03:34 AM
downthesun01
Re: Need help solving simple integral
Thanks. I just got it myself using integration by parts.

$u=3x$, $du=3dx$, $dv=\frac{1}{(1+x)^{4}}$, $v\frac{-1}{3(1+x)^{-3}}$