Solution

ID: past-exam-of-the-mathematics-course-of-the-year-2-of-the-natural-sciences-course-of-the-university-of-cambridge/2020/paper-1/7/c/solution

If is analytic on and inside a positively oriented simple closed contour except for finitely many isolated poles strictly inside it, then the residue theorem states
There must be no singularity on the contour. More generally each residue is multiplied by the contour's winding number about its point.

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