7. Given, S(r) = 3x + 2y2 + 2?. Calculate the following: (a) grad S(r)at the point (1,2,3). [5 Mar (b) the directional derivative of f(r) at (1,2,3) in the direction of the unit vector 1 (2,2,1) 3 (c) the maximum rate of change of the function at (1.2.3) and its direction. [2 Mar [3 Mar