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Homework Help: A Kronecker Delta problem

  1. Oct 7, 2012 #1
    1. The problem statement, all variables and given/known data

    [PLAIN]http://postimage.org/image/s7m1kohst/ [Broken][/PLAIN]

    2. Relevant equations

    The Kronecker Delta = 1 ; if i=j

    The Kronecker Delta = 0 ; i (not equal) j

    3. The attempt at a solution

    I have no idea what to do from here, or even if I did this first step right?
    [PLAIN]http://postimage.org/image/t3d3u9qg7/ [Broken][/PLAIN]
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 7, 2012 #2
    Still no luck on my own :(
  4. Oct 7, 2012 #3


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    Homework Helper

    Okay so expanding your sum :

    [tex]\sum_{i=1}^{3}a_iδ_{ij} = a_1δ_{1j} + a_2δ_{2j} + a_3δ_{3j}[/tex]

    Note that the only term which survives is the term [itex]a_jδ_{jj}[/itex] where i=j, but [itex]δ_{jj} = 1[/itex] as per the Delta Kronecker. So [itex]a_jδ_{jj} = a_j[/itex]

    Are you sure that's the question? I feel as if you're missing something. Some important intervals are not mentioned here.
  5. Oct 7, 2012 #4
    Thats the entire problem...im still confused from ur response, but I feel u gave me a good nudge in the right direction. thx
    Last edited: Oct 7, 2012
  6. Oct 7, 2012 #5
    That's the entire problem...hmmm
  7. Oct 7, 2012 #6
    I solved it for good, I understand it now. many thanks. The Kronecker Delta has the role of a substitution operator, basically replacing a repeated indice
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