所以f(x)=2x3-3x2+1,f'(x)=6x(x-1).令f′(x)=0,解得x=0或x=1.列表如下:
x | (-∞,0) | 0 | (0,1) | 1 | (1,+∞) |
f′(x) | + | 0 | - | 0 | + |
f(x) | ↗ | 極大值 | ↘ | 極小值 | ↗ |
當(dāng)x=1時,函數(shù)f(x)取得極小值f(1)=0.
(2)∵f′(x)=6x2-6ax=6x(x-a),
∴①當(dāng)a=0時,f′(x)=6x2≥0,函數(shù)f(x)在(-∞,+∞)上單調(diào)遞增;
②當(dāng)a>0時,f′(x)=6x(x-a),f′(x)、f(x)隨x的變化情況如下表:
x | (-∞,0) | 0 | (0,a) | a | (a,+∞) |
f′(x) | + | 0 | - | 0 | + |
f(x) | ↗ | 極大值 | ↘ | 極小值 | ↗ |
③同理可得,當(dāng)a<0時,函數(shù)f(x)在(-∞,a)上單調(diào)遞增,在(a,0)上單調(diào)遞減,在(0,+∞)上單調(diào)遞增.
綜上所述,當(dāng)a=0時,函數(shù)f(x)的單調(diào)遞增區(qū)間是(-∞,+∞);
當(dāng)a>0時,函數(shù)f(x)的單調(diào)遞增區(qū)間是(-∞,0)和(a,+∞),單調(diào)遞減區(qū)間是(0,a);
當(dāng)a<0時,函數(shù)f(x)的單調(diào)遞增區(qū)間是(-∞,a)和(0,+∞),單調(diào)遞減區(qū)間是(a,0).