解:
\(\frac{\partial f}{\partial x} = -2x\mathrm{e}^{-y} \Rightarrow f(x,y) = -x^2\mathrm{e}^{-y} + \varphi(y) \)。则\(\frac{\partial f}{\partial y} = x^2\mathrm{e}^{-y} + \varphi^\prime(y) = \mathrm{e}^{-y}x^2 - (y + 1)\mathrm{e}^{-y}\)
则\(\varphi^\prime(y) = -(y + 1)\mathrm{e}^{-y}\)
\(\Rightarrow \varphi(y) = (y + 2)\mathrm{e}^{-y} + C\)
则
\(f(x,y) = -x^2\mathrm{e}^{-y} + (y + 2)\mathrm{e}^{-y} + C\)
又\(f(0,0) = 2\),\(\Rightarrow C = 0\)
则\(f(x,y) = -x^2\mathrm{e}^{-y} + (y + 2)\mathrm{e}^{-y} \)。
\(\begin{cases}
\frac{\partial f}{\partial x} = -2x\mathrm{e}^{-y} = 0 \\
\frac{\partial f}{\partial y} = \mathrm{e}^{-y}(x^2 - y - 1) = 0
\end{cases} \Rightarrow \begin{cases}
x = 0 \\
y = -1
\end{cases}\)
则驻点\((0, -1)\)
\(f_{xx} = -2\mathrm{e}^{-y}, f_{xy} = 2x\mathrm{e}^{-y}, f_{yy} = \mathrm{e}^{-y}(x^2 - y - 1) - \mathrm{e}^{-y} = \mathrm{e}^{-y}(x^2 - y) \)
在点\((0, -1)\)处\(A = -2\mathrm{e}, B = 0, C = -\mathrm{e}\)
则\(AC - B^2 > 0, A < 0\),从而\( f(x,y) \)在\((0, -1)\)处有极大值,且极大值为
\(f(0, -1) = \mathrm{e}\)
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