Separate Variables Differential Eq. of Cubic Power

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Homework Help Overview

The discussion revolves around solving a first order non-linear ordinary differential equation given by dy/dx = x^2 /(1+y^2). Participants are exploring the implications of the solution, particularly regarding the expression of y in explicit form and the potential for multiple solutions involving imaginary numbers.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the integration of the equation and the resulting implicit form of the solution. Some express concern about the complexity of solving for y explicitly, particularly due to the involvement of imaginary numbers and multiple roots. Others suggest considering the implicit form or expressing x as a function of y instead.

Discussion Status

There is an ongoing exploration of the best approach to handle the solution. Some participants have provided guidance on rewriting the equation and have referenced external resources for solving cubic equations. However, there is no explicit consensus on the preferred method for proceeding with the solution.

Contextual Notes

Participants note the challenges associated with solving for y explicitly and the potential complications arising from the nature of cubic equations. There is also mention of the original poster's familiarity with cubic solutions tutorials, which may not align with the current problem's requirements.

knowLittle
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Homework Statement


When possible express the general solution in explicit form.
Solve dy/dx =x^2 /(1+y^2)

Homework Equations


This is a first order non-linear ordinary differential equation.


The Attempt at a Solution


dy(1+y^2) = x^2 dx
Integration both sides returns:
y+ (y^3 )/3= (x^3)/3 +C
Now, I am aware that there is more than one solution for y involving imaginary numbers. Can someone help me in the next step or direct me to a site?
I have seen cubic solutions tutorial, but they involve equations of the form: Ax^3+Bx^2+Cx+D=0

Thank you.
 
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knowLittle said:

Homework Statement


When possible express the general solution in explicit form.
Solve dy/dx =x^2 /(1+y^2)

Homework Equations


This is a first order non-linear ordinary differential equation.

The Attempt at a Solution


dy(1+y^2) = x^2 dx
Integration both sides returns:
y+ (y^3 )/3= (x^3)/3 +C
Now, I am aware that there is more than one solution for y involving imaginary numbers. Can someone help me in the next step or direct me to a site?
I have seen cubic solutions tutorial, but they involve equations of the form: Ax^3+Bx^2+Cx+D=0

Thank you.

I really don't think you want to solve for y. With an expression like that I'd just leave in the implicit form you already have, or maybe express x as a function of y instead. Don't try to use the cubic formula. It's a mess.
 
Last edited:
Yes, I am aware that it is kinda difficult to solve for 'y' and that's why I wanted to try it out. It involves imaginary numbers and many roots.
If someone can point me in the right direction, that would great.
 
Luckily, this is a seperable equation, which means you can rewrite it as
$$(1+y^2)dy = x^2dx.$$
Now, what can you do to get rid of those pesky differentials?
 
Thank you, tiny-tim. I usually use latex for big equations, but I thought it wouldn't be a big deal.

I was thinking that I could solve it like your wikipedia link... this will be interesting. Thanks.
 
YawningDog27 said:
Luckily, this is a seperable equation, which means you can rewrite it as
$$(1+y^2)dy = x^2dx.$$
Now, what can you do to get rid of those pesky differentials?
You really need to read through the thread. The OP has already done this and has gotten a solution.
 

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