Formula:115

Digital Library of Mathematical Functions ID 1.5.E21

${\displaystyle{\displaystyle\frac{{\partial}^{2}f}{{\partial x}^{2}}\frac{{\partial}^{2}f}{{\partial y}^{2}}-\left(\frac{{\partial}^{2}f}{\partial x\partial y}\right)^{2}>0\quad\mbox{ at $(a,b)$}.}}$

Symbols List

• ${\displaystyle{\displaystyle(\NVar{a},\NVar{b})}}$:
• ${\displaystyle{\displaystyle\frac{\partial\NVar{f}}{\partial\NVar{x}}}}$: partial derivative of $$f$$ with respect to $$x$$
• ${\displaystyle{\displaystyle\partial\NVar{x}}}$: partial differential of $$x$$
 

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