(1)f'(x)=2xex-1+x2ex-1+3ax2+2bx=xex-1(x+2)+x(3ax+2b),
由x=-2和x=1为f(x)的极值点,得
f′(?2)=0 f′(1)=0.
即
?6a+2b=0 3+3a+2b=0
解得
a=?
1 3 b=?1.
(2)由(1)得f(x)=x2ex?1?
x3?x2,1 3
故f(x)?g(x)=x2e x?1?
x3?x2?1 3
x3+x2=x2(ex?1?x).2 3
令h(x)=ex-1-x,则h'(x)=ex-1-1.(9分)
令h'(x)=0,得x=1.(10分)h'(x)、h(x)随x的变化情况如表:
x | (-∞,1) | 1 | (1,+∞) |
h'(x) | - | 0 | + |