c) In each of the following, Classify the given partial differential equations as hyperbolic, parabolic, or elliptic. a?u a u a?u (i) (ii) + 6 +9 %3! ay? axy au (ii) (xy + 1) + (x + 2y) +x y'u = 0 ay (iv) = 0; ais constant at (6 marks)