2?x |
x?1 |
函數(shù)f(x)的定義域?yàn)椋?,+∞),令f′(x)=0,求得x=2,
∵當(dāng)x∈(1,2)時(shí),f′(x)>0,當(dāng)x∈(2,+∞)時(shí),f′(x)<0,
∴f(x)在(1,2)內(nèi)是增函數(shù),在(2,+∞)上是減函數(shù)
∴當(dāng)x=2時(shí),f(x)取最大值f(2)=0.
(2)函數(shù)f(x)=ln(x-1)-k(x-1)+1沒(méi)有零點(diǎn),
即函數(shù)y=ln(x-1)的圖象與函數(shù)y=k(x-1)-1的圖象沒(méi)有交點(diǎn).
①當(dāng)k≤0時(shí),由于函數(shù)y=ln(x-1)圖象與函數(shù)y=k(x-1)-1圖象有公共點(diǎn),
∴函數(shù)f(x)有零點(diǎn),不合要求.
②當(dāng)k>0時(shí),f′(x)=
1 |
x?1 |
1+k?kx |
x?1 |
k(x?
| ||
x?1 |
令f′(x)=0,得x=
k+1 |
k |
k+1 |
k |
1 |
k |
∴f(x)在(1,1+
1 |
k |
1 |
k |
∴f(x)的最大值是f(1+
1 |
k |
∵函數(shù)f(x)沒(méi)有零點(diǎn),∴-lnk<0,求得k>1.
綜上可得,實(shí)數(shù)k的取值范圍為(1,+∞).