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Homework Help: Double integral using the dirac delta

  1. May 21, 2009 #1
    1. The problem statement, all variables and given/known data

    Need to integrate using the dirac delta substitution:
    [tex]
    \int_{-\infty}^{\infty}\int_{-\infty}^{\infty}\!x^2\cos(xy)\sqrt{1-k^2\sin^2(y)}\, dx\, dy
    [/tex]

    2. Relevant equations
    [tex]\cos(xy) = \frac{1}{2}\left(e^{ixy} + e^{-ixy}\right)[/tex]

    [tex]\delta\left[g(t)\right] =
    \frac{1}{2\pi}\int_{-\infty}^{\infty}\!e^{ikg(t)}\,dk[/tex]

    3. The attempt at a solution

    1) First I tried replacing cos with the exponents, this allowed breaking the integral into two (almost identical ;) ) parts.
    2) Next I should use the second formula (the one with delta) and replace exp with delta, which would help me to get rid of the x-parts...

    but the problem is how can I substitute delta when I have something like this (how to deal with the x^2 ???):
    [tex]\frac{1}{2\pi}\int_{-\infty}^{\infty}\!x^2e^{ix(y)}\,dx[/tex]
     
  2. jcsd
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