Then I multiply out
I would assume U sub at this point
But I am not sure, what or how I should bring along with the SEC
Just in case a picture helps...
... where (key in first spoiler) ...
Hope this helps - if not, someone will probably show the sub with differentials. However, I say...
Don't integrate - balloontegrate!
Balloon Calculus; standard integrals, derivatives and methods
Balloon Calculus Drawing with LaTeX and Asymptote!