Find general solution, 1st order ODE

In summary, the conversation discusses a homework problem involving finding a general solution for a given equation. The equation is identified as a Bernoulli equation and is manipulated to try and solve it, but the conversation ends with the person being stuck and unable to solve it.
  • #1
2h2o
53
0

Homework Statement



Find a general solution.

Homework Equations



[tex] 2x\frac{dy}{dx}+y^{3}e^{-2x}=2xy[/tex]

The Attempt at a Solution



Looks like a Bernoulli equation to me, after some algebra:

[tex]\frac{dy}{dx}+\frac{y^{3}}{2xe^{2x}}=y[/tex]

[tex]\frac{dy}{dx}+\frac{y}{2xe^{2x}}=y^{-1}[/tex]

so with [tex]n=-1[/tex]
[tex]v=y^{2}, y=v^{1/2}, \frac{dy}{dx}=\frac{1}{2}v^{-1/2}\frac{dv}{dx}[/tex]

[tex]\frac{1}{2}v^{-1/2}}\frac{dv}{dx}+\frac{v^{1/2}}{2xe^{2x}}=v^{-1/2}[/tex]

[tex]\frac{1}{2}\frac{dv}{dx}+\frac{v}{2xe^{2x}}=1[/tex]

[tex]\frac{dv}{dx}+\frac{v}{xe^{2x}}=2[/tex]

Now an integrating factor:

[tex]\mu=exp[\int{x^{-1}e^{-2x}dx}][/tex]

And that's where I get stuck. This doesn't look like any elementary integral I've learned how to solve, and wolfram|alpha gives me something called the "exponential integral" which we haven't been taught. So I've done something wrong, but I don't see it.

Thanks for any insights.
 
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  • #2
Ok, I think I found my error: I forgot to divide the dy/dx by y^2 when I obtained y^-1 as the RHS. No wonder I wound up with a nonelementary integral. However, I'm still stuck.

I don't recognize this equation, and manipulating it around trying to "force it" to be in first-order linear, homogeneous, or bernoulli hasn't helped. So I'm stuck.

This is where I am, and don't recognize it:

[tex]\frac{dy}{dx}+\frac{y^{3}}{2xe^{2x}}=y[/tex]
 
  • #3
Isn't that separable? Split up the differentials?
 
  • #4
This is just another Bernoulli type ODE isn't it?
 

1. What is a first order ODE?

A first order ODE (ordinary differential equation) is a mathematical equation that involves a single independent variable and its derivatives. It describes how a function changes over time or space.

2. What is a general solution?

A general solution is a set of mathematical expressions that satisfy the given first order ODE. It includes all possible solutions to the equation, which may contain arbitrary constants.

3. How do you find the general solution to a first order ODE?

To find the general solution to a first order ODE, you need to use techniques such as separation of variables, integrating factors, or substitution methods. These methods allow you to rearrange the equation and solve for the dependent variable in terms of the independent variable.

4. Can a first order ODE have multiple solutions?

Yes, a first order ODE can have multiple solutions. The general solution includes all possible solutions, which may contain arbitrary constants. These constants can take on different values, resulting in different specific solutions.

5. What is the difference between a general solution and a particular solution?

A general solution includes all possible solutions to the first order ODE, while a particular solution is a specific solution that satisfies the equation with given initial conditions. A particular solution can be obtained by substituting specific values for the arbitrary constants in the general solution.

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