解答:解(1)∵f′(x)=3ax2+2bx+c,且y=f′(x)的图象经过点(?2,0),(,0),
∴?,
∴f(x)=ax3+2ax2-4ax,
由图象可知函数y=f(x)在(?∞,?2)上单调递减,在(?2,)上单调递增,在(,+∞)上单调递减,由f(x)极小值=f(?2)=a(?2)3+2a(?2)2?4a(?2)=?8,解得a=?1,
∴f(x)=-x3-2x2+4x由(1)得f′(x)=-3x2-4x+4=-(3x+2)(x-2),
∴f′(x)=0,则x=?2或x=
x |
(-∞,-2) |
-2 |
(?2,) |
|
(,+∞) |
f'(x) |
- |
0 |
+ |
0 |
- |
f(x) |
单调递减 |
-8 |
单调递增 |
|
单调递减 |
|
∴函数f(x)的单调递减区间是(?∞,?2)和(,+∞),单调递增在区间是(?2,), |
极小值是?8,极大值是. |
|
|
(2)要使对x∈[-3,3]都有f(x)≥m
2-14m恒成立,
只需
f(x)min≥m2?14m即可.
由(1)可知
函数y=f(x)在[?3,?2)上单调递减,在(?2,)上单调递增,在(,3]上单调递减且f(-2)=-8,f(3)=-3
3-2×3
2+4×3=-33<-8,
∴f(x)
min=f(3)=-33-33≥m
2-14m?3≤m≤11
故所求的实数m的取值范围为{m|3≤m≤11}.