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Homework Help: Complicated delta function integral

  1. Oct 29, 2012 #1
    1. The problem statement, all variables and given/known data
    Hi guys ,please look at the integral on the attachement.Does anyone have seen this integral before ?

    2. Relevant equations
    We have the following two properties :

    ∫δ'(x-x0)f(x) dx =-f'(x0)

    δ(x^2-a^2)= {δ(x-a) +δ(x+a)}/2a

    3. The attempt at a solution
    Please help ,i have studied all the physics books available and im starting searching for the answer in books of history.Im desperate .I couldn't find this integral nowhere no matter how hard i would search.

    so can one say :∫{f(x){δ'(x-a) +δ'(x+a)}/2a } dx and then split this integral in two :

    ∫{f(x)δ'(x-a)/2a + f(x)δ'(x+a)}/2a} dx and now we use the first property i gave above
    to get:
    {-f'(a)-f'(-a)}/2a =-f'(a)/a ~ this just a guess and in the last step i have assumed :

    f'(a)=f'(-a) is this last property true ?

    This was just a guess ,and i need a definite answer so please don't reply if you are not sure about the answer.

    Attached Files:

  2. jcsd
  3. Oct 30, 2012 #2


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    Are you sure of that? I get {δ(x-a) +δ(x+a)}/4a
  4. Oct 31, 2012 #3


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    I'd agree with the OP.

    This is not true in general. For example, take f(x) = x^2. f'(x) = 2x, which does not possess the property f'(x) = f'(-x).
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