i could get the directional derivative which is -12. but how to get the unit vector out of it?Quote:

Consider the function http://webwork.asu.edu/webwork2_file...4fc9a409d1.png.

Find the the directional derivative of http://webwork.asu.edu/webwork2_file...faee426371.png at the point http://webwork.asu.edu/webwork2_file...67a2a39eb1.png in the direction given by the angle http://webwork.asu.edu/webwork2_file...f0ab38ba21.png. Find the unit vector which describes the direction in which http://webwork.asu.edu/webwork2_file...faee426371.png is increasing most rapidly at http://webwork.asu.edu/webwork2_file...67a2a39eb1.png.