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Homework Help: Diff eq, need a simple step explained

  1. Sep 8, 2010 #1
    So its not a problem, but a step in an example that I need explained. The section is solutions by substitutions and its an example of solving a homogeneous DE.

    Step goes from:
    [tex]\left(x^{2}+u^{2}x^{2}\right)dx+\left(x^{2} - ux^{2}\right)\left[udx + xdu\right]=0[/tex]

    to:
    [tex]x^{2}\left(1 + u\right)dx + x^{3}\left(1-u\right)du=0[/tex]

    It had previously set y=ux, a few steps back.
     
  2. jcsd
  3. Sep 8, 2010 #2

    Mark44

    Staff: Mentor

    Just expand the expressions above, and simplify.
    [tex](x^2 + u^2x^2 + x^2u - u^2x^2)dx + (x^3 - ux^3)du = 0[/tex]
     
  4. Sep 8, 2010 #3
    Thank you... I dont know why I didn't see this before.. Ok I feel stupid. :/
     
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