Good source of problems for multivariate calculus

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Hi,

I have this qualifying exam coming up in about a month for my Ph.D. program in math. I just noticed that my European undergraduate education covered nothing about actually calculating any tricky integrals. It was only about Riemann sums and proving properties of the integral which I know very well including the theory of differential forms.

I noticed that old exams had some questions where you had to evaluate some tricky integral. Does anyone know a good source of tricks and problems for integrals i.e. something where you could get to hammer on non-trivial problems involving Green's Gauss' and Stokes' theorem?

Thanks.