1 |
3 |
∴f′(x)=x2-4=(x+2)(x-2),
令f′(x)=0,解得x=-2,或x=2,
列表討論,得:
x | (-∞,-2) | -2 | (-2,2) | 2 | (2,+∞) |
f′(x) | + | 0 | - | 0 | + |
f(x) | ↑ | 極大值 | ↓ | 極小值 | ↑ |
∵函數(shù)f(x)=
1 |
3 |
28 |
3 |
∴f(-2)=
8 |
3 |
28 |
3 |
解得m=4.
(2)由m=4,得f(x)=
1 |
3 |
當(dāng)x=2時(shí),f(x)取極小值f(2)=-
4 |
3 |
1 |
3 |
28 |
3 |
1 |
3 |
x | (-∞,-2) | -2 | (-2,2) | 2 | (2,+∞) |
f′(x) | + | 0 | - | 0 | + |
f(x) | ↑ | 極大值 | ↓ | 極小值 | ↑ |
1 |
3 |
28 |
3 |
8 |
3 |
28 |
3 |
1 |
3 |
4 |
3 |