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Multivariable CalculusHardVector Calculus

Vector Calculus · Hard problem

Let DD be the annulus 1≤x2+y2≤41\le x^2 + y^2\le 4, and let ∂D\partial D be its boundary with the positive orientation (outer circle counterclockwise, inner circle clockwise). Evaluate ∮∂D−x2y dx+xy2 dy\displaystyle\oint_{\partial D} -x^2y\,dx + xy^2\,dy. Give your answer in terms of π\pi.