Question

函数y=sin(3x+)cos(x-)+cos(3x+)cos(x+)的图象的一条对称轴是直线(    )

A.x=           B.x=                C.x=-           D.x=-

Answer 1

解析:y=sin(3x+)cos(-x)+cos(3x+)·sin(-x)=sin(3x++-x)=sin(2x+)=cos2x.

令2x=kπ(k∈Z),

∴x=.

令k=-1,得x=-.

答案:D