# Going further with integration by parts. Don't know whether to proceed further or not

1. Jan 28, 2013

### Ein Krieger

Hey guys,

Need you push to proceed further with integration by parts:

∫e3x*3*x2*ydx=y∫e3x*3*x2dx

setting u=3*x2-------du=6*x dx
dv= e3*xdx--- v= 1/3* e3*x

∫ e3*x*3*x2*ydx=y*(3*x2* 1/3* e3*x-∫6*x*1/3* e3*xdx)
=y*(3*x2* 1/3* e3*x-6/3*∫x*e3*xdx)
u=x---du=dx
dv=e3*xdx---v=1/3*e3*x
∫ e3*x*3*x2*ydx=y*(3*x2* 1/3* e3*x-6/3*(x*1/3*e3*x-∫1/3e3*x)

2. Jan 28, 2013

### Ein Krieger

Re: Going further with integration by parts. Don't know whether to proceed further or

How can we go further with solution as exp(3*x) repeats all the time?

3. Jan 28, 2013

### Staff: Mentor

Re: Going further with integration by parts. Don't know whether to proceed further or

You've done all the hard work. ∫e3xdx is easy, using a simple substitution.

4. Jan 29, 2013

### HallsofIvy

Re: Going further with integration by parts. Don't know whether to proceed further or

If you have $\int x^n f(x)dx$, where "f" is easy to integrate any number of times (and the "nth" integral of $e^{3x}$ is $(1/3^n)e^{3x}$), just continue taking $u= x^n$, $dv= f(x)dx$. Everytime du will have x to a lower power until, eventually, it is just $x^0= 1$.