1.选Bπ/2+2kπ<π/6-2x<3π/2+2kπ-2π/3-kπ<x<-π/6-kπ取k=-1,则π/3<x<5π/6,所以选B2.选DA:y=cos2x在(0,π/2)为单调减,是偶函数B:y=|sin2x|是以π/2为周期的偶函数,在(0,π/4)为增函数,在(π/4,π/2)为减函数C:y=|cosx|在(0,π/2)为减函数.3.选Cy=(3cos 展开
1.选Bπ/2+2kπ<π/6-2x<3π/2+2kπ-2π/3-kπ<x<-π/6-kπ取k=-1,则π/3<x<5π/6,所以选B2.选DA:y=cos2x在(0,π/2)为单调减,是偶函数B:y=|sin2x|是以π/2为周期的偶函数,在(0,π/4)为增函数,在(π/4,π/2)为减函数C:y=|cosx|在(0,π/2)为减函数.3.选Cy=(3cosx+1)/(cosx+2)=[3(cosx+2)-5]/(cosx+2)=3-5/(cosx+2)当cosx=-1时y最小为-2当cosx=1时y最大为4/3 收起
