need help w/ differential equation

Discussion in 'The Lounge' started by j_Reez, Nov 9, 2004.

  1. j_Reez

    j_Reez Private E-2

    hi everyone, this might sound a bit funny but i need some help with a homework problem. its a second order nonlinear DE. This is what i got so far...

    problem: xy'' -x(y')^2 = y'

    what i have so far:

    u=y' and du/dx=y''

    du/dx - u^2 = (1/x)u

    int[(1/u)-u]du = int[1/x]dx <-------------int[ ] means integrate inside

    ln u - (1/2)u^2 = ln x +c

    ok, now is what ive done so far correct? what do i do next?
     
  2. Diet of Nothing

    Diet of Nothing Private E-2

    It's too late for me to think this all the way through, but I did spot one possible mistake.

    After you substitute in u and du/dx for y' and y'' you divide through by x. This operation is not allowed unless you have stated that x != 0. Otherwise you may just be dividing by zero.
     

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