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#1 2007-05-20 13:04:14
- Old_Steve
- Member
- Registered: 2007-05-15
- Posts: 17
Non-Linear Diff. Eq. - Help!
It seems they make all the examples in the books easy. Here is a first order diff. eq that I need to solve:
(3y^2 + 2xy)dx - (2xy+x^2)dy = 0
I appreciate any help!
Answer is (y^2/x^3)+(y/x^2)=c but I can't seem to get there.
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#2 2007-05-20 16:00:51
- Stanley_Marsh
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- Registered: 2006-12-13
- Posts: 345
Re: Non-Linear Diff. Eq. - Help!
you can make it
Last edited by Stanley_Marsh (2007-05-20 16:15:06)
Numbers are the essence of the Universe
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#3 2007-05-20 22:03:51
- Old_Steve
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- Registered: 2007-05-15
- Posts: 17
Re: Non-Linear Diff. Eq. - Help!
Thanks! I had more problems with the algeraic conversion at line 2 than anything.
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#4 2007-05-21 10:18:34
- Old_Steve
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- Registered: 2007-05-15
- Posts: 17
Re: Non-Linear Diff. Eq. - Help!
Can you tell me why C must be ln(C) at the end? Why when you integrate is it not just + C?
I have other problems I am working that will only work when C = ln(C)
Last edited by Old_Steve (2007-05-21 10:19:24)
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#5 2007-05-21 11:00:19
- mathsyperson
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- Registered: 2005-06-22
- Posts: 4,900
Re: Non-Linear Diff. Eq. - Help!
It's just made that way to make the problem easier. C and ln C are just constants. The values of C are different, but C is arbitrary so it doesn't matter.
If it helps you understand, you could write +C in the integration step and then change that to +ln A in the next step, where A is a constant.
Why did the vector cross the road?
It wanted to be normal.
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#6 2007-05-21 13:07:04
- Old_Steve
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- Registered: 2007-05-15
- Posts: 17
Re: Non-Linear Diff. Eq. - Help!
Thanks for explaining.
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