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Need quick help with Series, it will only take a few seconds!

  1. Nov 27, 2012 #1
    So the differential equation I have to solve using power series is
    y''-xy=0 when x0 = -1

    So i set it up
    Ʃ(n+2)(n+1)an+2(x+1)n - x Ʃ an(x+1)n

    I know how to generally solve equations like this, but I never solved one like this, where I have to distribute the x ... x(x+1)n ... I just need to figure this part out (I know I left out the n=0 to ∞)
     
  2. jcsd
  3. Nov 27, 2012 #2
    Ok I figured it out using a cheap (but valid) math trick... in case anyone is wondering...

    xƩan(x+1)n = (x+1-1)Ʃan(x+1)n

    Now the x+1 can be distributed to give -Ʃan(x+1)n+1

    ...anyone care to double check me on this?
     
  4. Nov 27, 2012 #3

    Mute

    User Avatar
    Homework Helper

    Yep, that's the trick you want to use.
     
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