Results 1 to 2 of 2

Thread: Differential Equations (first order)

  1. #1
    Junior Member
    Apr 2010

    Differential Equations (first order)

    I need to solve:

    1) (2x-y+5)*dy/dx + x -2y +3=0

    here, I made the derivative the subject then substituted to get rid of the constants... in the end I got
    (x+y+2)^3 = (y-x-8/3)/(k^2) where lnk= C (constant of integration)
    Is this right? a friend got (x-y+8/3)*k^2 on the right-hand side

    any help is much appreciated
    Last edited by cassius; Dec 8th 2010 at 01:07 PM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Dec 2010
    I dont know what you mean- you might be making this more complicated than necessary.
    If you make the substition z=-x, then you have a differential equation of the form
    A(z,y) + B(z,y)dz/dy = 0
    where $\displaystyle A_y = B_z$ [not my favoured notation but Im not familiar with the BBcodething for partial derivatives: anyway it equals -2 in this example]
    this is a standard equation with solvable method described in good textbooks I guess .

    [ Simpler if you are not familiar with the above: y=-x+C is a solution by inspection, and you can work out C]
    Last edited by mr fantastic; Dec 25th 2010 at 06:22 PM. Reason: Restored deleted post. User banned.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: May 7th 2011, 10:26 AM
  2. Replies: 2
    Last Post: May 18th 2009, 03:49 AM
  3. Replies: 2
    Last Post: Feb 23rd 2009, 05:54 AM
  4. Replies: 5
    Last Post: Jul 16th 2007, 04:55 AM
  5. Replies: 3
    Last Post: Jul 9th 2007, 05:30 PM

Search Tags

/mathhelpforum @mathhelpforum