问题 选择题
设函数f1(x)=log4x-(
1
4
)x
f2(x)=log
1
4
x-(
1
4
)x
的零点分别为x1、x2,则(  )
A.0<x1x2<1B.x1x2=1C.1<x1x2<2D.x1x2≥2
答案

∵函数f1(x)=log4x-(

1
4
)xf2(x)=log
1
4
x-(
1
4
)x
的零点分别为x1、x2

∴0<x2<1<x1

f1(x1)=log4x1-(

1
4
)x1=0,f2(x2)=log
1
4
x2-(
1
4
)
x2
=-log4x2-(
1
4
)
x2
=log4
1
x2
-(
1
4
)
x2
=0,

(

1
4
)x2 >(
1
4
)
x1
,∴log4x1 <log4
1
x2
,即x1
1
x2

∴0<x1x2<1,

故选A.

单项选择题
单项选择题