f'(x)=-x^2-2x/3+5/3
令f'(x)≤0
-x^2-2x/3+5/3≤0
3x^2+2x-5≥0
(x-1)(3x+5)≥0
x≥1或x≤-5/3
函数的单调递减区间为(-∞,-5/3]U[1,+∞)；单调递增区间为[-5/3,1]