Question

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f(x, y) is a differentiable function with f(20, -100) = (5, -2). Let g(x, y) = f(xy2, 2x2y) and calculate f(5, -2). Let n = (4, 2). What is the directional derivative (5, -2)? Use the above to approximate g(4, 0) if g(5, -2) = (2, -1).