Let f(x,y, z) denote a differentiable function of three variables. It is known that = 9 at the point (1,5, 21), and that the maximum value of the directional derivative of f at the point (1,5, 21)...

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Extracted text: Let f(x,y, z) denote a differentiable function of three variables. It is known that = 9 at the point (1,5, 21), and that the maximum value of the directional derivative of f at the point (1,5, 21) occurs in the direction of the vector 27 + 37 + 8K. Find the maximum value of the directional derivative of f at the point (1,5, 21). Give your answer correct to two decimal places. af %3D