2k=-3a，ka=-6。 The solution is: a=2, k=-3 or a=-2, k=3 (s).
∴ analytical formula of this function: y=-3x.
2 、( 1)S = 1/2×| OA |×y = 1/2×6×(8-x)= 24-3x(0 & lt； x & lt8)
(2)S(5)=24-3×5=9
(3) No, because the area must be greater than 0.