Let f : R R be differentiable and define u:
by u(x,y) := show that u satisfies the partial differential equation
+ = (sin y + x cos y)u ?
Similarly for , then add the two, obviously... pic in a mo.
... where (key in spoiler) ...
Spoiler:
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Don't integrate - balloontegrate!
Balloon Calculus; standard integrals, derivatives and methods
Balloon Calculus Drawing with LaTeX and Asymptote!