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Homework Help: A tricky 2nd ODE nonhomo delta=0 help needed

  1. May 11, 2009 #1
    1. The problem statement, all variables and given/known data
    solve the initial value problem:
    y(0)=1, y'(0)=1


    2. Relevant equations

    3. The attempt at a solution

    The way I tried to achieve is to solve the corresponding homo equation first:
    y''+8.4y'+17.64y=0, which gives yc;

    Then try to find yp, generally I would assume a yp=Ae-4.2x, but from the yc got above, clearly yp=Ae-4.2x or yp=Ae-4.2xx is not good. If I add one more 'x' in yp assumption,in which it seems A has to be 0, which is not right either....

    Any idea? Or I made some mistake?

  2. jcsd
  3. May 11, 2009 #2


    Staff: Mentor

    Assuming that the work you show is correct, yp = Ax2e-4.2x is the right choice. Plug it into your DE and solve for A.
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