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Soient \(P \in \C[X]\) et \(f : {\R^2} \to \C, {(x,y)} \mapsto {P(x+iy).}\) Montrer que \(\frac{\partial^2 f}{\partial x^2} + \frac{\partial^2 f}{\partial y^2} = 0\).
Soient \(P \in \C[X]\) et \(f : {\R^2} \to \C, {(x,y)} \mapsto {P(x+iy).}\) Montrer que \(\frac{\partial^2 f}{\partial x^2} + \frac{\partial^2 f}{\partial y^2} = 0\).