Hello,

No, but you didn't substitute at allOriginally Posted byFirstone

$\displaystyle \sqrt{x}=u \implies du=\frac{dx}{2 \sqrt{x}} \implies dx=2 \sqrt{x} ~du \neq \frac{2 du}{\sqrt{x}}$

Transform your integral : every x has to disappear. So as soon as you encounter $\displaystyle \sqrt{x}$, change it into u. If there was $\displaystyle x$ that you encounter, then $\displaystyle x=u^2$ and substitute too.

And then integrate by parts as recommended. Don't forget to either change the boundaries of the integral, either to substitute back u.

P.S. : please next time, post a new thread. It may be useful for some other people (and my PM box is overwhelmed by all these messages lol!)