To compute $\int_{6}^{11}\int_{10}^{15} \left( \frac{9xy}{\sqrt{x^{2}+y^{2}+8}} \right) dxdy$ you do the u substitution:
u =
du =

$\int_{6}^{11}\int_{10}^{15} \left( \frac{9xy}{\sqrt{x^{2}+y^{2}+8}} \right) dxdy =$

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