Math Challenge - October 2018

[benorin]

The entire thing is positive, continuous and bounded, so Fubini applies.

^This.
That is what I should have answered to the Q: "Justify the initial equality by which theorem?" Except for at the origin, a singlet of measure zero. But that the integrand was unbounded thereat seemed to justify a little caution on my part; that and not knowing which Fubini Theorem variant to use. But then you both are experts, @fresh_42 strikes me as a seasoned Analysis prof, or the equivalent in terms of wit.

 

[benorin]

@fresh_42 added 7. e) to post #63 (done)