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Differential Equation Method OF UNDETERMINED COEFF

  1. Oct 16, 2011 #1
    1. The problem statement, all variables and given/known data
    I hav been trying to solve this differential equation by Method of Undetermined Coefficients for a long time.

    y"-2y'-3y=-3te^(-t) ....................

    We are supposed to guess a solution then differentiate and go from there. I guessed
    y = (At + B)e^(-t) ............. but this does not work. ........... can someone help me on this ... I have also tried y = Ae^(-t) but this also doesnt work. Is it possible the book answer is wrong ?


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 16, 2011 #2

    vela

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    You first need to solve the homogeneous equation. What solution do you get to that?
     
  4. Oct 16, 2011 #3

    LCKurtz

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    Of course it's possible the book is wrong. It is also possible that you are wrong. You shouldn't have to "guess" what to try if you have the complementary solution.

    I suggest you re-check your work for Ae-t. And if you get an answer you can always check it for yourself by plugging it into the DE.
     
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