Hi folks,

I am having a hard timne getting my head around a problem involving double integrals, was hoping someone more learned the myself could nudge me in the right direction.

ok, suppose we have,

,

,

Now, define as

Now, in simple terms this is just

Its when I substitute for that i get problems...

I can see that the this extra factor comes from integrating twice.... but i dont understand why it comes about .

Any help would be most appreciated.