Double integral using the dirac delta

[plaes]

Homework Statement

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]

Homework 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]

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]

 

[Nino MMP]

\, dyIf I can figure out how to do it, the rest should be easy ;) Any hints/ideas would be really appreciated.