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JKPolk 02-15-2007 06:00 PM

Help With The Maths Please!
 
Been doing Calc all day... can someone help me out with this integral? It would mean the world!


RandomPscho 02-15-2007 09:07 PM

Re: Help With The Maths Please!
 
Sorry I cannot help,
But how did you write the formula? What program did you use?

super kid 02-15-2007 09:08 PM

Re: Help With The Maths Please!
 
What do you need to solve for?

LifereaperX 02-15-2007 09:13 PM

Re: Help With The Maths Please!
 
Message removed due to hi19hi19

wickedawesomeful 02-15-2007 09:15 PM

Re: Help With The Maths Please!
 
*head explodes*

...Seriously though. Ow. That hurt my head just looking at it.

Doug31 02-15-2007 09:21 PM

Re: Help With The Maths Please!
 
Is there any more information you can give us on this problem? Right now, it looks like a trig substitution or something, but I don't see how to do it, unless you know more about this problem.

LifereaperX 02-15-2007 09:23 PM

Re: Help With The Maths Please!
 
Message removed due to hi19hi19

LifereaperX 02-15-2007 09:25 PM

Re: Help With The Maths Please!
 
Message removed due to hi19hi19

Chrissi 02-15-2007 09:25 PM

Re: Help With The Maths Please!
 
I can't tell if you guys are being idiots on purpose or what.

If had taken another year of math in university I'd be able to help you out. Unfortunately, I probably can't tell you anything you don't already know, as I only just barely touched on integrals.

johnnyhoney0 02-15-2007 09:27 PM

Re: Help With The Maths Please!
 
That looks like a double integral if I had to say anything about it, or, perhaps, an integral with more than one variable. Way above what I can help with.

Can you try separating the integrals by variable and then integrating them?[/pretending to know what I'm talking about]

Kit- 02-15-2007 09:32 PM

Re: Help With The Maths Please!
 
If you don't have to evaluate it the proper way, you can always recognize that it has perfect radial symmetry and convert it to a single integral.

spyke252 02-15-2007 09:33 PM

Re: Help With The Maths Please!
 
lets see
can you use a triangle with sides a, r, and (a^2+r^2)^.5?

LifereaperX 02-15-2007 09:39 PM

Re: Help With The Maths Please!
 
Message removed due to hi19hi19

GuidoHunter 02-15-2007 09:48 PM

Re: Help With The Maths Please!
 
I'd say trig substitution as well, but it's been way too long since I did Cal II or Cal III, so I have no idea which to do.

I also spy a Jacobian, not that that's of any import, here.

--Guido

http://andy.mikee385.com

spyke252 02-15-2007 09:56 PM

Re: Help With The Maths Please!
 
LifeReaper, this is the CT forum... please stop?

EDIT: your math is wrong anyways.
4!=-2^(2)
exponents take precedence over most other mathematical signs, so -2^(2) equates to -4 not 4.

JKPolk 02-15-2007 10:07 PM

Re: Help With The Maths Please!
 
You DO spy a Jacobian. Nice eye. I wrote the expression MSWord using Equation Editor, and just SSd it and imageshacked it.

The equation is written correctly, it is solvable. It is a double integral, so one has to evaluate the inner integral first with respect to r, and then evaluate the result with respect to theta. I don't think trig substitutions would really help, as this is already in polar coordinates and using trig would probably only create a small catastrophe.

I've tried using u substitution and integration by parts but I just can't seem to crack the code.

Quote:

Originally Posted by lifereaper
Oh! All the variables equal zero! That appears to work, since those "less-than-or-equal-to" signs are there.

The less than or equal to signs give the range of integration, so the integral with respect to r goes from 0 to a/sqrt(2) and the integral with respect to theta goes from 0 to 2Pi.

And to those who are asking what to solve for, it should come out to be a number with respect to the variable 'a,' I'm not really trying to solve for anything, seeing as this isn't an equation.

Thanks for your input, I'm gonna keep plugging away at this until I pass out probably!

LifereaperX 02-15-2007 10:20 PM

Re: Help With The Maths Please!
 
Message removed due to hi19hi19

Chrissi 02-15-2007 10:27 PM

Re: Help With The Maths Please!
 
Quote:

Originally Posted by LifereaperX (Post 1196176)
They wouldn't take precedence over the negative sign... It would be -2*-2, which equals positive 4...

No, actually it would be - (2*2).

Which = -4.

What you are saying is (-2)^2, rather than -2^2.

JKPolk 02-16-2007 12:21 AM

Re: Help With The Maths Please!
 
OK so I eventually got it. I split it up into two integrals, distributing the r at the end into each factor and integrating the first and second sections separately. Thanks for the suggestions on how to tackle it!

Could_Strife007 02-16-2007 02:12 AM

Re: Help With The Maths Please!
 
If this was differential calc we probably would have been of a bit more help, but then of course you probably wouldn't be asking for help


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