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La funksjonen $f:X\\subseteq\\mathbb{R}^3\\rightarrow\\mathbb{R}$ være deriverbar i $\\mathbf{a}$.

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La $f_x(\\mathbf{a})=f_y(\\mathbf{a})=f_z(\\mathbf{a})=0$.

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La $d_1=f_{xx}(\\mathbf{a})$, $d_2=\\left| \\begin{array}{ccc} f_{xx}(\\mathbf{a}) & f_{xy}(\\mathbf{a})  \\\\ f_{yx}(\\mathbf{a}) & f_{yy}(\\mathbf{a}) \\end{array} \\right|$,   $d_3=\\left| \\begin{array}{ccc}  f_{xx}(\\mathbf{a}) & f_{xy}(\\mathbf{a}) & f_{xx}(\\mathbf{a}) \\\\ f_{yx}(\\mathbf{a}) & f_{yy}(\\mathbf{a}) & f_{yz}(\\mathbf{a}) \\\\ f_{zx}(\\mathbf{a}) & f_{zy}(\\mathbf{a}) & f_{zz}(\\mathbf{a})\\end{array} \\right|$,  

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Velg matchende påstander

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