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Homework Help: Just couldnt figure this out =

  1. Oct 31, 2008 #1
    why the equivalence??????

    there must be some formula for this...just i donno.
    i really need some hints!!! thank you guys!
     

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  2. jcsd
  3. Oct 31, 2008 #2

    gabbagabbahey

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    Homework Helper
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    The derivative operator [itex]\frac{\partial^j}{\partial x^j}[/itex] is acting only on x...the j=0 derivative is just the zeroith order derivative of x, which is x. The j=1 derivative is [itex]\frac{\partial}{\partial x}x=1[/itex]. Since this is a constant, all higher order derivatives are zero and so all the j>1 terms in each of the sums is zero. You are left with only the j=0 and j=1 terms which you can write out explicitly to obtain the expression on the right.
     
  4. Oct 31, 2008 #3
    THANK YOU SOOOOOOOOOOO MUCH!

    Now i understand why it goes like that!!!
     
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