Solution

ID: past-exam-of-the-mathematics-course-of-the-year-2-of-the-natural-sciences-course-of-the-university-of-cambridge/2010/paper-1/7/solution

Evaluate the derivative along real and imaginary increments. For a holomorphic function, both give the same value:
Equating real and imaginary parts yields the Cauchy-Riemann equations

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