4. Consider the R2 - R function f given by f(x, y) = x2 + xy -2y2 Let V be the tangent plane to the graph of f at the point (-1, 1, -2) 4.1 Calculate the rate of change in f at (x, y) = (-1, 1) in the direction of the vector (5, 12). (5) 4 2 Calculate the maximum rate of change of f at (x, y) = (-1, 1) (2)