Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2009/paper-1/11/a/ii/solution

For the real inverse hyperbolic tangent, take and . Its logarithmic expression gives
The same derivative holds on a differentiable complex branch away from its singularities.

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