Problem 3 (14 points) Let f (x, y, z ) = 3 x2 +y2+ 2 2 , if (x, y, z) # (0, 0, 0) 0. if (x, y, z) = (0, 0, 0) (a) Use the definition to find the directional derivative of the function f at (0, 0, 0) in the direction (a, b, c), where a2 + b2 + c2 = 1. (b) Use Lagrange Multipliers to find the maximal and minimal directional derivatives