Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2019/ii/paper-4/23h/e/solution

Use the Poisson integral to choose a smooth harmonic function on the unit disk whose boundary value is . Seek in the form , which is the standard homogenization of Dirichlet boundary data. Then and, since ,
Part (d) gives a unique such , and hence
is the unique weak solution with boundary value .

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