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#1 2008-03-06 05:54:35
- Archit
- Member
- Registered: 2008-03-06
- Posts: 2
Can't solve this integral. (substitution?)
Hello all I need some help with this problem, I just can't get.
I have an integral like this:
I started like this:
I'm positive I can't simplify the integrand any further, and so I'm sure that I need to make a substitution to solve it, but I'm going absolutely mad trying to find a good substitution to make.
I would REALLY appreciate some help with this. Thanks alot, Archie
Last edited by Archit (2008-03-06 06:08:22)
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#2 2008-03-06 05:59:08
- Daniel123
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- Registered: 2007-05-23
- Posts: 663
Re: Can't solve this integral. (substitution?)
You've gone a bit wrong with the codes there. Have a look at the sticky thread at the top of the help me section to learn LaTeX.
To make it clearer for everyone, I think you mean:
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#3 2008-03-06 06:05:44
- Archit
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- Registered: 2008-03-06
- Posts: 2
Re: Can't solve this integral. (substitution?)
Sorry, seeing all the 'useful characters' at the top of the page, I assumed this site didn't have LaTeX, and missed the sticky thread at the top. I'll re-type in LaTeX.
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#4 2008-03-06 09:53:14
- mathsyperson
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- Registered: 2005-06-22
- Posts: 4,900
Re: Can't solve this integral. (substitution?)
Try substituting u = 100-x.
Sorry if I'm stating the obvious (you've probably tried that already), but I'm pretty sure it does work.
Why did the vector cross the road?
It wanted to be normal.
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#5 2008-03-06 11:53:47
- Archit
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- Registered: 2008-03-06
- Posts: 2
Re: Can't solve this integral. (substitution?)
I forgot to write that the x in the sqrt is squared too, so its 100-x^2. Sorry about that
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#6 2008-03-08 00:09:17
- mathsyperson
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- Registered: 2005-06-22
- Posts: 4,900
Re: Can't solve this integral. (substitution?)
As TheDude said before we moved servers, that actually makes things a little easier.
Using u = 100-x² gives that dx = -du/2x.
The x's cancel and you're left with
.Why did the vector cross the road?
It wanted to be normal.
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#7 2008-03-08 00:19:43
- Daniel123
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- Registered: 2007-05-23
- Posts: 663
Re: Can't solve this integral. (substitution?)
Mathsyperson, we resolved this yesterday before we moved servers 
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#8 2008-03-08 00:33:30
- mathsyperson
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- Registered: 2005-06-22
- Posts: 4,900
Re: Can't solve this integral. (substitution?)
I knew that it had been answered yesterday, but I couldn't remember whether Archit had seen the answer. Still, restating something never hurts.
(And it took all of my willpower to not say that twice 
)
Why did the vector cross the road?
It wanted to be normal.
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