Explain why the function is differentiable at the given point. f(x, y) = 4 + x ln(xy − 9), (5, 2) the partial derivatives are fx(x, y) = correct: your answer is correct. and fy(x, y) = correct: your answer is correct. , so fx(5, 2) = 10 correct: your answer is correct. and fy(5, 2) = 25 correct: your answer is correct. both fx and fy are continuous functions for xy > incorrect: your answer is incorrect. and f is differentiable at (5, 2). find the linearization l(x, y) of f(x, y) at (5, 2). l(x, y) =