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Using the Frobenius

  1. Aug 1, 2009 #1
    Am I missing something in the Frobenius method??

    1. The problem statement, all variables and given/known data

    Use the method of Frobenius to find solutions near x= 0 of each of the differential equations.

    3. The attempt at a solution

    x^2 y'' + (2x^2 + 3x)y' + (x-(5/4))y = 0

    My work is as follows:


    I don't know where I went wrong, or what I'm doing wrong. My r's are correct of 1/2 and -5/2.

    I use r =1/2 first, and when I evaluate for n = 1 I get...

    ..x^1/2 [c_o - c_o/2 x + c_o/5 x^2 + 2c_o /5 + ...]

    the answer in the back of the book has the last line in that pic. I know that I haven't finished solving for the other r, but the portion that is circles with the arrow, does not match what I have so far. I noticed they have their sigma starting at n=0. I tried evaluating them for the n's but my answer differ. :(

    please help.
    Last edited: Aug 2, 2009
  2. jcsd
  3. Aug 3, 2009 #2


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    Homework Helper
    Gold Member

    Re: Am I missing something in the Frobenius method??

    There's your problem. Remember, the r=-5/2 series will also have terms of order x1/2, x3/2, etc. When you add the terms of these orders from both your r=1/2 and r=-5/2 series together, you should get the right answer.
  4. Aug 4, 2009 #3
    I'll go ahead and do that, will post back.

    Thanks gabba.
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