17 If M and m are the maximum and minimum values of f(x,y) = xy subject to 4x2 + y2 = 8, then M -m= 1 4x²+4-8 y = 1 (3x) x=x (24) = = (a) (b) (C) (d) (e) -3 0 2 y 4 24 8x