# Differential equations problem

1. Jul 16, 2008

### sahen

solve the following ivp
xy' - y = 3xe^2y/x
y(1)=-1

how can i get rid of e ? does anybody help me ?
thanks in advance.

2. Jul 16, 2008

### CompuChip

I assume that e is just the Euler number 2.7...
Why would you want to get rid of it? And why then don't you ask: "how can I get rid of 3?"

3. Jul 16, 2008

### Defennder

It's hard to read what you wrote. Do you mean: $$xy' - y = \frac{3xe^2y}{x}$$?

4. Jul 17, 2008

### sahen

It should be xy' - y = 3xe$$^{2y/x}$$
I guess i need to study more thanks for your help.

5. Jul 17, 2008

### CompuChip

Ah, so the equation is
[tex]
x y' - y = 3 x \exp\left[ \frac{2y}{x} \right]
[tex]
... that makes the problem significantly more complex
I'm not even sure there is an exact solution.

6. Jul 17, 2008

### crystalplane

For the IVP problem, you should find I(X)
you may get I(x)=e^x dx
then you multiply I(X) on both sides and you can solve the problem i guess

7. Jul 17, 2008

### Hurkyl

Staff Emeritus
On the contrary, it suggests an obvious thing to try. And due to good fortune*, it works.

Really, this is one of those problems that (at least for the beginner) should fall into the category of "this looks complicated -- there is only one thing I could possibly do, and I just have to hope it works".

*: Okay, fine, it's more likely that it was rigged to work.

Last edited: Jul 17, 2008
8. Jul 18, 2008

### Defennder

It takes a substitution to make things a lot easier as Hurkyl said.

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