Register to reply

Integration by parts

by Rasine
Tags: integration, parts
Share this thread:
Rasine
#1
May10-07, 02:50 PM
P: 214
intergrate (ln(x))^2

so i set u=(lnx)^2...which makes du=2lnx(1/x)

then i set dv=dx...which makes v=x

according to the formula for integration by parts i have

x(lnx)^2- integral x(2lnx)(1/x)
simplifying it i get x(ln)^2-2intergral lnx


and here is where i am stuck....what i the integral of lnx?
Phys.Org News Partner Science news on Phys.org
Experts defend operational earthquake forecasting, counter critiques
EU urged to convert TV frequencies to mobile broadband
Sierra Nevada freshwater runoff could drop 26 percent by 2100
cristo
#2
May10-07, 02:53 PM
Mentor
cristo's Avatar
P: 8,317
The derivative of (lnx)^2=(2lnx)/x.

[edit: of course that's you've written... i glanced and say ln(1/x)... sorry ]

A hint for integrating lnx; use parts, taking dv=dx and u=lnx
neutrino
#3
May10-07, 02:54 PM
P: 2,046
How about integration-by-parts once again? :)

quasar987
#4
May10-07, 03:00 PM
Sci Advisor
HW Helper
PF Gold
quasar987's Avatar
P: 4,771
Integration by parts

xln(x) - x looks good from where I'm standing.

I just wondered "what function gives ln(x) when differentiated? Well ln(x)' = 1/x. So what if I try xln(x)? Now I get ln(x) + 1. So I need to add something to the mix that gives -1 when differentiated." Hence xln(x) - x.
Rasine
#5
May10-07, 03:06 PM
P: 214
ohhh yes......do integration by part again........

thank you!


Register to reply

Related Discussions
Integration problems. (Integration by parts) Calculus & Beyond Homework 5
Integration by parts Calculus & Beyond Homework 1
Integration by parts Calculus 6
Integration by Parts Calculus & Beyond Homework 1
Using Integration by Parts Calculus & Beyond Homework 5