Select which of the following statements are true. From the 6 options, select all that apply 0 If the discriminant D of a function f(x, y) is always zero, then Vf = 0. 0 If fix = fyy then ever critical point of f(x, y) is a saddle point. Vf 0 If u = then Daf = Vf. If (a, b) is a critical point of f(x, y), then (a, b) is a critical point of fr (x, y). If (a, b) is a solution to the Lagrange equations Vf(a, b) = >Vg(a, b), then at the point (a, b) we have |Vf . Vgl = ||Vfill| Vall. If fix(x, y)