设函数f(x)=x2ex-1+ax3+bx2,已知x=-2和x=1为f(x)的极值点.(1)求a和b的值;(2)设g(x)=23x3?x2

2024-12-02 06:25:16
推荐回答(1个)
回答(1):

(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.

?6a+2b=0
3+3a+2b=0

解得
a=?
1
3
b=?1.

(2)由(1)得f(x)=x2ex?1?
1
3
x3?x2

f(x)?g(x)=x2e x?1?
1
3
x3?x2?
2
3
x3+x2x2(ex?1?x)

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 +