3) in which f is increasing most rapidly, and find the rate at which it is increasing. s) Find the directional derivative of f at (-2, 5, 3) in the direction (8, 1, -4). (c) (2 points) Is there a direction (x, y, 0) at this point in which f remains constant? Put another way, is there a direction that is parallel to the xy-plane such that Duf = 0? If so, find such a direction. If not,explain why no such direction exists.

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