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Yay differential equations...
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WGP guy2 View Drop Down
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I play the Bag Pipes

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    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
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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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Fire in the disco

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Do your own homework.
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Strike 1 6/25

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I cut bait on calculus right before Diff Eq.
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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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WGP guy2 View Drop Down
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Meh... I just neatly went through every method my professor has taught and showed none of them works.  Hopefully that is good enough.
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¤ Råp¡Ð F¡rè ¤ View Drop Down
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This title is just way too old

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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.


Edited by ¤ Råp¡Ð F¡rè ¤ - 27 January 2009 at 12:53am
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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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¤ Råp¡Ð F¡rè ¤ View Drop Down
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This title is just way too old

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Points: 1090 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ¤ Råp¡Ð F¡rè ¤ Quote  Post ReplyReply Direct Link To This Post 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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WGP guy2 View Drop Down
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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.
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¤ Råp¡Ð F¡rè ¤ View Drop Down
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This title is just way too old

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Oh, forget what I was talking about then. I thought you were trying to accomplish something completely different.
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This forum is exactly what I think of when I desire assistance with my calculus homework.
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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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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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I suck at math and for some idiotic reason, decided to take an online math class this semester.

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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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We get it, you take Calc.

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WGP guy2 View Drop Down
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Originally posted by Benjichang Benjichang wrote:

We get it, you take Calc.


Diff eq =/ calc.  I'm past calc. 
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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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