已知函數(shù)f(x)=13x3?(4m?1)x2+(15m2?2m?7)x+2在(-∞,+∞)上是增函數(shù),則m的取值范圍是( ) A.m<-4或m>-2 B.-4<m<-2 C.2<m<4 D.m<2或m>4
已知函數(shù)
f(x)=x3?(4m?1)x2+(15m2?2m?7)x+2在(-∞,+∞)上是增函數(shù),則m的取值范圍是( ?。?br/>A. m<-4或m>-2
B. -4<m<-2
C. 2<m<4
D. m<2或m>4
數(shù)學人氣:880 ℃時間:2019-08-18 23:37:53
優(yōu)質(zhì)解答
對
f(x)=x3?(4m?1)x2+(15m2?2m?7)x+2求導,得
f′(x)=x
2-2(4m-1)x+(15m
2-2m-7)
已知函數(shù)
f(x)=x3?(4m?1)x2+(15m2?2m?7)x+2在(-∞,+∞)上是增函數(shù)
故f′(x)>0
即求使x
2-2(4m-1)x+(15m
2-2m-7)>0的m的取值范圍
可以看出函數(shù)開口向上,使△<0即可
對[-2(4m-1)]
2-4(15m
2-2m-7)<0求解,得
2<m<4
故選C
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