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Today's problem

\frac{d}{d x} [- 4 x - \frac{5}{x ^{2}}]

The hard one · double XP

For f (x, y) = 4 x^{2} + 2 x y^{2} - 11 y^{2}, find f_{xx} f_{y y} - (f_{x y})^{2} at (0, 2)