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Very simple D.E.

  1. Sep 16, 2005 #1
    Find a solution to the following D.E.

    [tex]\frac{dy}{dx} + \frac{x}{y}=0[/tex]


    Separate variables...

    [tex]ydy = -xdx[/tex]

    Integrate both sides...


    Multiply both sides by 2, and here is where my problem arises...


    Stuck. [itex]x^2[/itex] will always be positive, so after applying the negative, I can't take the squareroot. It has to be a simple mistake. Please give a small bit of help or a small hint. :confused:
  2. jcsd
  3. Sep 16, 2005 #2
    Aaargh... nearly there...


    Does this ring a bell?
  4. Sep 18, 2005 #3


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    Staff Emeritus
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    Gold Member

    Is there some reason you must restrict yourself to the reals? Even with the constant of integration which you need (as above) there is the possibility of a complex solution. A complete problem statement will include the boundary conditions or initial values. You have not provided a complete problem statement. Without that. your solution is complete with the addion of the constant of integration.
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