**Answers to quiz 6**

1. The Laplace equation f_{xx} + f_{yy} = 0 in polar coordinates x = r cosθ, y = r sinθ is f_{rr} + f_{r}/r + f_{θθ}/r^{2} = 0 (Eq. 11.19)

2. If f(x,y) satisfies f_{xy} = 0 then by integration with respect to y we observe that f_{x} is a function φ of x only, and by subsequent integration with respect to x, f is the integral of φ(x) plus an arbitrary function of y: f = g(x) + h(y), g, h are arbitrary functions.

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