| (Oral Mines-Ponts) Déterminer les {f\in \mathcal{C}^{2}(\mathbb{R}^{2},\ \mathbb{R})} telles que {\dfrac{\partial ^{2}f}{\partial x^{2}}-4\dfrac{\partial ^{2}f}{\partial x\partial y}+3\dfrac{\partial ^{2}f}{\partial y^{2}}=0} |
| (Oral Mines-Ponts) Déterminer les {f\in \mathcal{C}^{2}(\mathbb{R}^{2},\ \mathbb{R})} telles que {\dfrac{\partial ^{2}f}{\partial x^{2}}-4\dfrac{\partial ^{2}f}{\partial x\partial y}+3\dfrac{\partial ^{2}f}{\partial y^{2}}=0} |