若点(1,3)为曲线 =a(x)^3+b(x)^2 的拐点,则a,b值应为 ()-|||-A =dfrac (9)(2), =-dfrac (3)(2)-|||-书 =-dfrac (3)(2) =dfrac (9)(2)-|||-C =-3, b=6-|||-D a=2 b=1