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 Post subject: Integration? - Math
PostPosted: Fri May 09, 2008 9:31 pm 
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Compsognathus
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Joined: Thu Jul 24, 2003 8:03 pm
Posts: 1040
I guess this question fits here, right then, I am stuck with pure mathematics, how the hell am I supposed to integrate lnx/x^2 ??? ive spent hours and hours it just doesn't integrate right! :x

Ive been using integration by parts, which is required by the question

INT u dv/dx dx = uv - INT v du/dx dx


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 Post subject: Re: Integration? - Math
PostPosted: Sat May 10, 2008 2:12 am 
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Velociraptor
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Location: Canberra, Australia
Sure, here we go:

So you have f(x) = ln(x)x^-2

Let u = ln(x)

So, du/dx = x^-1
Thus, du = x^-1 dx

Now, let dv/dx = x^-2

Therefore, integrate dv/dx to get v = -x^-1

Now for integration by parts:

INT u.dv = uv - INT v.du -Sub in the above results.

= ln(x).-x^-1 - INT -x^-1 . x^-1 . dx
= ln(x).-x^-1 - INT -x^-2 . dx
= ln(x).-x^-1 - x^-1 + C - But lets just ignore the constant C.
= ln(x).-x^-1 - x^-1

Therefore, INT u.dv = ln(x).-x^-1 - x^-1 = -x^-1(ln(x)+1)

Hope that helps.

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 Post subject: Re: Integration? - Math
PostPosted: Sat May 10, 2008 3:38 am 
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T-Rex Killer
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I had thought this would be a question regarding numerical integration and computers, given the section where it was being asked... turned out to be simple mathematical integration instead.

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 Post subject: Re: Integration? - Math
PostPosted: Sat May 10, 2008 8:16 am 
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Albertosaurus
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:o thanks god I gave up maths after my GCSEs :P

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 Post subject: Re: Integration? - Math
PostPosted: Sat May 10, 2008 12:48 pm 
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Compsognathus
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Joined: Thu Jul 24, 2003 8:03 pm
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Hey thanks Chris! :) I had figured out how to do this, iam still learning to integrate by parts, turned out i wasn't using the formula properly. But thanks again! Iam sure of the way to use the formula now.


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 Post subject: Re: Integration? - Math
PostPosted: Sat May 10, 2008 6:03 pm 
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Albertosaurus
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Joined: Wed Mar 05, 2003 9:28 pm
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This makes me miss math


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 Post subject: Re: Integration? - Math
PostPosted: Mon May 12, 2008 7:59 pm 
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-=TresCom Developer=-
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Everyone's favorite integral:

INT sqrt(tanx)dx

:P

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