
#1
Jun1806, 05:16 AM

P: 27

i cant find it anywhere. plz help. i need to kno the inegration of lnx to find an area. plz help thx




#2
Jun1806, 07:16 AM

HW Helper
P: 1,422

Integration is a Calculus topic, and therefore, should not be posted in the Precalculus section.
Anyway, to integrate ln(x), we use Integration by Parts (have you covered Integration by Parts yet?), i.e: [tex]\int u dv = uv  \int v du[/tex] We often use Integration by Parts, when no other methods can solve the integral. So, we want to integrate this: [tex]\int \ln (x) dx[/tex] We then let u = ln(x), and dv = dx So that implies du = dx / x, and v = x. Substitute all those into the formula, we have: [tex]\int \ln (x) dx = x \ln (x)  \int x \times \frac{dx}{x} = ...[/tex] Can you go from here? :) 



#3
Jun1806, 09:07 PM

P: 27





#4
Jun1906, 02:09 PM

Sci Advisor
HW Helper
P: 1,996

how to integrate ln(x)
It can be done without integration by parts. Try integrating over y instead of x, that is consider your graph to be x=exp(y).




#5
Feb1809, 04:08 PM

P: 1

You cant integrate ln(x) by parts!!!!!!!!




#6
Feb1809, 04:29 PM

P: 18

u=lnx dv= dx
du= 1/x dx v=x =xlnxintegral(1)dx = xlnxx+c lnx using IBP:) 



#7
Feb1809, 05:34 PM

PF Gold
P: 280

This site is great for checking your work when integrating:
http://integrals.wolfram.com It will not give you fully worked out answers but it will give you the final answer. Of course, your teacher will want you to solve problems showing your work all the way through, but this is still a great site. 


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