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Yay differential equations...

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Topic: Yay differential equations...
Posted By: WGP guy2
Subject: Yay differential equations...
Date Posted: 26 January 2009 at 11:10pm
I've been working on this problem for the past 3 hours and have 7 pages of work, but still no solution.  Anyone good with diff eq?

(x^2)(dy/dx) = y^2 + xy



Replies:
Posted By: choopie911
Date Posted: 26 January 2009 at 11:31pm


Posted By: Rambino
Date Posted: 26 January 2009 at 11:33pm
Let me think...   The last time I did one of those was ...   oh yeah - a very long time ago.  You are a couple of decades too late for my help.  But it is a fun class.
 
:)


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Posted By: High Voltage
Date Posted: 26 January 2009 at 11:43pm
Do your own homework.

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Posted By: Uncle Rudder
Date Posted: 26 January 2009 at 11:58pm
I cut bait on calculus right before Diff Eq.

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Posted By: sinisterNorth
Date Posted: 27 January 2009 at 12:02am
Heh...if I ever took/had to take Calc, I'd try to help. But alas, the only math I have to take in college is statistics. And psychology statistics at that.

Good luck.


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Posted By: WGP guy2
Date Posted: 27 January 2009 at 12:20am
Meh... I just neatly went through every method my professor has taught and showed none of them works.  Hopefully that is good enough.


Posted By: ¤ Råp¡Ð F¡rè ¤
Date Posted: 27 January 2009 at 12:44am
Originally posted by WGP guy2 WGP guy2 wrote:


(x^2)(dy/dx) = y^2 + xy


(x^2)(dy/dx) = y^2 + xy
2x = 2ydy + xdy + y
2x - y = dy (2y + x)
dy = (2x - y) / (2y + x)

I think it's something like that.
file:///C:%5CDOCUME%7E1%5CRWOLTE%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml -

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Posted By: ThatGuitarGuy
Date Posted: 27 January 2009 at 12:55am
21 minutes to find a cartoon online explaining differential equations.

I really wonder if Choop had that one waiting to post, or if he had to search for it.


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Posted By: ¤ Råp¡Ð F¡rè ¤
Date Posted: 27 January 2009 at 12:58am
Originally posted by ThatGuitarGuy ThatGuitarGuy wrote:

21 minutes to find a cartoon online explaining differential equations.

I really wonder if Choop had that one waiting to post, or if he had to search for it.


Lol, it was on the Digg front page.


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Posted By: WGP guy2
Date Posted: 27 January 2009 at 1:14am
Originally posted by ¤ Råp¡Ð F¡rè ¤ ¤ Råp¡Ð F¡rè ¤ wrote:

Originally posted by WGP guy2 WGP guy2 wrote:


(x^2)(dy/dx) = y^2 + xy


(x^2)(dy/dx) = y^2 + xy
2x = 2ydy + xdy + y
2x - y = dy (2y + x)
dy = (2x - y) / (2y + x)

I think it's something like that.


Umm...what?

It looks like you just did some algebra and pseudo-calculus.

To solve it it needs to go in the from Mdx + Ndy = 0

So it would be:

(y^2 + xy) dx - (x^2) dy = 0

I'm trying to find y(x)  the y in the original function will be an equation, not a number.

That solution is not exact, and needs to be for me to use one of the techniques I've been taught so far.  There must be some integrating factor that makes it exact, however the techniques to find integrating factors I've been taught so far all fail.

I'm pretty sure it involves some substitution and special integrating factor, but I can't figure out what they are.


Posted By: ¤ Råp¡Ð F¡rè ¤
Date Posted: 27 January 2009 at 1:32am
Oh, forget what I was talking about then. I thought you were trying to accomplish something completely different.

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Posted By: High Voltage
Date Posted: 27 January 2009 at 1:38am
This forum is exactly what I think of when I desire assistance with my calculus homework.

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Posted By: notXXscared
Date Posted: 27 January 2009 at 12:28pm
Originally posted by ¤ Råp¡Ð F¡rè ¤ ¤ Råp¡Ð F¡rè ¤ wrote:

I thought you were trying to accomplish something completely different.

Accomplish something completly different...as in the wrong answer?


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Posted By: Rambino
Date Posted: 27 January 2009 at 12:32pm
Originally posted by sinisterNorth sinisterNorth wrote:

And psychology statistics at that.
 
 
I hereby declare this class "not math."
 
(me = math snob)


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Posted By: Linus
Date Posted: 27 January 2009 at 12:44pm
I suck at math and for some idiotic reason, decided to take an online math class this semester.

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Posted By: pntbl freak
Date Posted: 27 January 2009 at 12:55pm
If you would have posted this a few years ago...I could have helped.  I dont remember anything about them now.

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Posted By: Benjichang
Date Posted: 27 January 2009 at 1:12pm
We get it, you take Calc.

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Posted By: WGP guy2
Date Posted: 27 January 2009 at 1:43pm
Originally posted by Benjichang Benjichang wrote:

We get it, you take Calc.


Diff eq =/ calc.  I'm past calc. 


Posted By: Rambino
Date Posted: 27 January 2009 at 1:44pm
Originally posted by WGP guy2 WGP guy2 wrote:

Originally posted by Benjichang Benjichang wrote:

We get it, you take Calc.


Diff eq =/ calc.  I'm past calc. 
 
I dunno.  I always figured DiffEq was like Calc 1.5.  I would definitely call it calculus, though.  But hey - semantics.


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Posted By: WGP guy2
Date Posted: 27 January 2009 at 2:17pm
Originally posted by Rambino Rambino wrote:

Originally posted by WGP guy2 WGP guy2 wrote:

Originally posted by Benjichang Benjichang wrote:

We get it, you take Calc.


Diff eq =/ calc.  I'm past calc. 
 
I dunno.  I always figured DiffEq was like Calc 1.5.  I would definitely call it calculus, though.  But hey - semantics.


I wouldn't think so.  Sure, it takes a lot of calculus to do the problems, but the techniques used to solve differential equations aren't calculus really, they just use calculus.  From my perspective, what you said could be akin to calling calculus algebra, or algebra arithmetic.  You use the latter for the former, but they aren't the same deal.

Anyway, if someone asks I usually tell them I'm in calc 4, not purposely but because I'm used to saying I'm in calc x.


Posted By: new jersey
Date Posted: 27 January 2009 at 8:20pm
Calc scares me.


Posted By: ammolord
Date Posted: 27 January 2009 at 9:02pm

*jaw drops* i thought algebra sucked. now i know where to come for help.



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Posted By: You Wont See Me
Date Posted: 28 January 2009 at 12:31am
The answer is undefined

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