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## Homework Statement

Hi

I wish to perform an integral of the form

[tex]

\int_0^a {\int_0^b {f\left( {x - y} \right)dxdy} }

[/tex]

What I do first is to define s := x-y, and ds = dx. Then we get

[tex]

\int_0^a {\int_{-y}^{b-y} {f\left( {s} \right)dsdy} }

[/tex]

Then I can define t := x+y, so dt = dy. Then I get

[tex]

\int_{x}^{x+a} {\int_{-y}^{b-y} {f\left( {s} \right)dsdt} }

[/tex]

I also have to multiply by 2, since it is the Jacobian of the transformation. But look at the limits: It doesn't seem to make things easier. Where am I going wrong?

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