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(2015?衡水模擬)關(guān)于x的函數(shù)f(x)=m(x2-4x+lnx)-(2m2+...

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時間:2024-08-17 09:47:17
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(2015?衡水模擬)關(guān)于x的函數(shù)f(x)=m(x2-4x+lnx)-(2m2+...【專家解說】:解:(1)函數(shù)f(x)=m(x2-4x+lnx)-(2m2+1)x+2lnx的導(dǎo)

【專家解說】:解:(1)函數(shù)f(x)=m(x2-4x+lnx)-(2m2+1)x+2lnx
的導(dǎo)數(shù)f′(x)=m(2x-4+1x)-(2m2+1)+2x,
由函數(shù)f(x)在(1,0)處的切線斜率為0,
即有f′(1)=0,f(1)=0,
即為2m2+m-1=0,且2m2+3m+1=0,
解得m=-1,
即有f(x)=-x2+x+lnx,
f(x)=-x2+x+lnx的導(dǎo)數(shù)為f′(x)=-2x+1+1x
=-2x2+x+12=-(2x+1)(x-1)x,
當(dāng)x>1時,f′(x)<0,f(x)單調(diào)遞減,
當(dāng)0<x<1時,f′(x)>0,f(x)單調(diào)遞增.
則有f(x)在x=1處取得極大值,也為最大值,且為0,
由于函數(shù)f(x)的圖象與直線y=k2-2k無公共點,則k2-2k>0,
解得k>2或k<0;
(2)設(shè)F(x)=f(x)-((p-2)x2+p+22x+2x-x2 )
=lnx-p2x-p+22x,
F′(x)=1x-p2+p+22x2=-px2+2x+(p+2)2x2,
當(dāng)p=0時,F(xiàn)′(x)=2x+22x2>0,F(xiàn)(x)在[1,2]遞增,F(xiàn)(1)=-1<0不成立,(舍)
當(dāng)p≠0時F′(x)=-p(x+1)(x-p+2p)2x2,
當(dāng)1+2p<-1,即-1<p<0時,F(xiàn)(x)在[1,2]遞增,F(xiàn)(1)=-p-1<0,不成立;
當(dāng)-1<1+2p≤1,即p<-1時,F(xiàn)(x)在[1,2]遞增,所以F(1)=-2p-2≥0,解得p≤-1,
所以,此時p<-1;
當(dāng)p=-1時,F(xiàn)(x)在[1,2]遞增,成立;
綜上,p的取值范圍是(-∞,-1].