已知定义域为R的偶函数f(x)在[0,+∞)上是增函数,且f()=0,则不等

已知定义域为R的偶函数f(x)在[0,+∞)上是增函数,且f()=0,则不等式f(log4x)>0的解集为

A.{x|x>2}                                                             B.{x|0<x

}

C.{x|0<x

x>2}                                            D.{x|x<1或x>2}

 

答案

解析一:取满足题干的特殊函数f(x),当x≥0时,f(x)=2|x|-1,并作出其图象.

借助于图象可直观知,f(x)的函数值区间为(-∞,-

)∪(,+∞).

f(log4x)>0

log4x或log4x<-

x>2或0<x

.

解析二:∵f(x)为偶函数,∴f(x)在(-∞,0)上为减函数.

f(

)=0得f(-)=0.

∴原不等式可化为

即log4x

或log4x<-.∴x>2或0<x.

答案:C


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