= //pull out a '1'

= //use integration by parts

=

=

=

Is pulling out a 1 in the first step a legitimate method when using integration by parts, or is it just a coincidence that it works? Thanks!

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- November 30th 2010, 05:59 PMGlitchIs this a legitimate way of finding the integral of lnx?

= //pull out a '1'

= //use integration by parts

=

=

=

Is pulling out a 1 in the first step a legitimate method when using integration by parts, or is it just a coincidence that it works? Thanks! - November 30th 2010, 06:00 PMdwsmith
Pull out a 1? There is a 1 in every equation since multiplying by 1 does nothing.

Just doing integration by parts will work. - November 30th 2010, 06:04 PMGlitch
I think my understanding of integration by parts isn't too good. :(

I'm not sure how to perform it without there being two functions to work with, which is why I pulled out the one. What's the proper way of dealing with this? - November 30th 2010, 06:07 PMdwsmith
If we have an x, there is always an implied 1. There is a one in every function you can think since multiplying by a 1 does nothing to an equation.

- November 30th 2010, 06:14 PMGlitch
So my method was right, but you don't think of it as pulling out a one? I just did that to help my head get around it.

- November 30th 2010, 06:15 PMdwsmith
Why pull out something that already exists?

- November 30th 2010, 06:23 PMTheCoffeeMachine
Is this what you're doing? If it's, then it's valid, of course:

- December 1st 2010, 01:56 AMGlitch
Yeah, that's what I'm doing. Thanks.