the function $\mathrm{f}$.
$D=\frac{\partial^{2} f}{\partial X_{1}^{2}} \cdot \frac{\partial^{2} f}{\partial X_{2}^{2}}-\left(\frac{\partial^{2} f}{\partial X_{1} \partial X_{2}}\right)^{2}0$

Question

the function $\mathrm{f}$.
$D=\frac{\partial^{2} f}{\partial X_{1}^{2}} \cdot \frac{\partial^{2} f}{\partial X_{2}^{2}}-\left(\frac{\partial^{2} f}{\partial X_{1} \partial X_{2}}\right)^{2}>0$

Quizplus · Accepted Answer

The given expression $D$ is the determinant of the Hessian matrix of a function $f$, which is used to determine the concavity or convexity of $f$ at a point, not the function itself.

The Function f\mathrm{f}f

The Function $\mathrm{f}$