Separable differential equation

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Homework Help Overview

The problem involves a differential equation of the form (x + 2y) dy/dx = 1, with an initial condition y(0) = 1. Participants are exploring whether it can be classified as a homogeneous equation and discussing the appropriate methods for separation or substitution.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Some participants attempt to separate the variables and question the classification of the equation as homogeneous. Others suggest using the substitution y = ux and discuss the necessary form dy/dx = f(x,y) for this approach to be valid.

Discussion Status

The discussion is ongoing, with participants offering various approaches and questioning the assumptions about the equation's form. There is no explicit consensus, but suggestions for potential methods have been provided, including the substitution and rewriting the equation.

Contextual Notes

Participants note the challenge of separating the equation and the requirement for it to be expressed in a specific form before applying certain methods. There is also mention of the original problem being taken directly from a textbook.

ch2kb0x
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Homework Statement


(x + 2y) dy/dx = 1, y(0) = 1


Homework Equations





The Attempt at a Solution



Problem is, I can't separate it. This might be a homogenous type? If so, how would I make it into the g(y/x) form.

Thank you.
 
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Start with u = y/x, or equivalently, y = ux. From this, find dy/dx.
 
Okay, so since you said y = ux, I am thinking that this is a homogenous equation...

However, if it is a homogeneous equation, before we can plug in y = ux, aren't we suppose to first have the equation in the form of dy/dx = f(x,y), where there exists a function such that f(x,y) is expressed g(y/x).

Then, AFTEr we can do the y=ux thing. correct me if I am wrong.
 
ch2kb0x said:
Problem is, I can't separate it. This might be a homogenous type? If so, how would I make it into the g(y/x) form.

Thank you.

Well, that is because it isn't a separateable equation... It isn't even an ODE. Sure it's right?
 
Yeah, copied exactly from textbook.
 
ch2kb0x said:
Okay, so since you said y = ux, I am thinking that this is a homogenous equation...

However, if it is a homogeneous equation, before we can plug in y = ux, aren't we suppose to first have the equation in the form of dy/dx = f(x,y), where there exists a function such that f(x,y) is expressed g(y/x).

Then, AFTEr we can do the y=ux thing. correct me if I am wrong.
You can write the equation as dy/dx = 1/(x + 2y), where the right side is a function of x and y. I'm just offering a suggested approach based on your first post. It may or may not work.
 
Yeah, it is a function of x and y, but I don't think it's in the g(y/x) form.
 
Mark44 said:
You can write the equation as dy/dx = 1/(x + 2y), where the right side is a function of x and y. I'm just offering a suggested approach based on your first post. It may or may not work.

To me it seems that you are suggesting a linear trial solution?
 
The OP said he wanted to put this into g(y/x) form, so that made me think of the substitution I suggested. I don't have access to my DE textbooks right now, so I don't have any more ideas on solving this one.
 

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