Help Solving a differential equation

In summary, the conversation discusses a differential equation (x+2y)y'=y and the use of substitution to solve it. However, it is mentioned that substitution may not be the best method and instead, rewriting the equation as y(dx/dy)=x+2y is suggested. It is also mentioned that the equation may not be exact, but can be made exact with an integrating factor.
  • #1
Giuseppe
42
0
Hello, i was wondering if someone can help me along with solving this differential equation.(x+2y)y'=y

I believe you use substitution. Right now I am setting my substitution to
v=(x+2y), but then when i follow through with my work, it doesn't simplify down to a seperable or first order linear equation. Am I doing something wrong?

-giuseppe
 
Last edited:
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  • #2
try this should make a nice linear in terms of x

divide the left side by y

then divide 1 by y' and you should end up with a linear in terms of x
 
  • #3
Rewrite this in the form M(x,y)dx + N(x,y)dy = 0. Then, check if this is an exact differential equation. If not, can you find an integrating factor to make it exact?

I don't think substitution works here. It's just not separable.
 
  • #4
This is NOT an exact equation either.

I like Valhalla's suggestion. You can rewrite it as

y(dx/dy)= x+ 2y which is a LINEAR equation for x as a function of y. If you really need y as a function of x, invert the function.
 
  • #5
I didn't say it was exact... I said he should check if it was exact. :smile:

It's easy enough to make it exact with an integrating factor though.

There is more than one way to skin a cat...
 

1. What is a differential equation?

A differential equation is a mathematical equation that involves an unknown function and its derivatives. It describes the relationship between the rate of change of a quantity and the quantity itself.

2. What is the purpose of solving a differential equation?

The purpose of solving a differential equation is to find the unknown function that satisfies the equation. This can help us understand and predict the behavior of systems in various fields such as physics, engineering, and economics.

3. What are the different methods for solving a differential equation?

There are several methods for solving a differential equation, including separation of variables, substitution, variation of parameters, and using differential equation solvers. The specific method used depends on the type and complexity of the equation.

4. How do I know if my solution to a differential equation is correct?

To check the correctness of a solution to a differential equation, you can substitute the solution back into the equation and see if it satisfies the equation. Additionally, you can use numerical methods or software to verify the solution.

5. Can differential equations be solved analytically or numerically?

Yes, differential equations can be solved both analytically and numerically. Analytical solutions involve finding an exact formula for the unknown function, while numerical solutions involve approximating the solution using algorithms and computing techniques.

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