Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2017/ii/paper-4/11f/d/solution

The continuous closed curve satisfies . It lies in the right half-plane, which admits a single continuous complex argument in . Since closes, this argument has equal endpoint values, giving . Additivity under multiplication then yields
The strict inequality ensures that the quotient stays in a region avoiding zero and admitting a single argument branch.

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