Find Singular Solution to dy/dx=x(1-y^2)^(1/2)

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Discussion Overview

The discussion revolves around finding a singular solution to the differential equation dy/dx = x(1 - y^2)^(1/2). Participants explore the nature of singular solutions in the context of this non-linear equation, considering both general and singular solutions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about how to find a singular solution after separating and integrating the given differential equation.
  • Another participant explains that singular solutions are "other" solutions not derived from the general solution and notes that they can envelop general solutions.
  • A participant suggests that if 1 - y^2 = 0, then y must be ±1, questioning whether these values are derived from the general solution.
  • A later reply proposes that plotting the general and singular solutions would clarify their relationship, indicating that visual representation can aid understanding.
  • An attached plot illustrates particular solutions of the form y(x) = sin(x^2/2 + c) alongside the singular solutions y(x) = 1 and y(x) = -1, highlighting how the singular solutions envelop the particular solutions.

Areas of Agreement / Disagreement

Participants appear to agree on the definition and nature of singular solutions, but there is no consensus on the specific methods to derive them or their relationship to the general solutions.

Contextual Notes

The discussion does not resolve the mathematical steps necessary to find the singular solution, nor does it clarify the assumptions involved in the separation and integration process.

andrewdavid
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Here is the differential equation I have: dy/dx=x(1-y^2)^(1/2) . I'm supposed to find a singular solution to that equation but I'm really not sure how to figure it out. I can separate and integrate it, but then what is the singular solution?
 
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andrewdavid said:
Here is the differential equation I have: dy/dx=x(1-y^2)^(1/2) . I'm supposed to find a singular solution to that equation but I'm really not sure how to figure it out. I can separate and integrate it, but then what is the singular solution?

For the equation:
[tex]y^{'}=x\sqrt{1-y^2}[/tex]

As you stated, you can separate variables, integrate, and find y(x). However, some non-linear equations have "other" solutions which are not derived from this general solution. These are called "singular solutions". Note you can divide by the radical assuming it's not zero. If it is zero, then:

[tex]1-y^2=0[/tex]

But if that's so, then what does that tell you y(x) has to be? Well, + or - 1 right? Are those derived from the solution you get when you separate variables and integrate? Singular solutions "envelop" general solutions. Check that out. Plot some examples of the general solutions and the singular solutions and see what I mean.
 
So how about a plot showing this Andrew? You know a plot really makes this all clear especially to others that may be new to this. I guess if you don't then I'll submit one in a day or so.
 
Attached is a plot of some examples of particular solutions of:

[tex]y(x)=\sin(\frac{x^2}{2}+c)[/tex]

and the two singular solutions y(x)=1 and y(x)=-1. Note how the singular solutions envelop the particular solutions.
 

Attachments

  • singular.JPG
    singular.JPG
    15 KB · Views: 860

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