Q1. Let (r, y) # (0,0). f(r) 0 (r, y) = (0, 0). Find all unit vector u such that Do f (0,0) exists. Q2. Let f(r, y) = arctan(r + y). a. Find the direction v, in terms of an unit vector, in which f changes most rapidly at (1, 1). b. Compute Def (1, 1). Q3. Compute the gradient for the following functions. a. f (r, y, = ) = sec(r + y) + b. f (r. y) = Ity I-V