cos(x+π/3)
=sin[π/2-(x+π/3)]
=sin(π/6-x)
=-sin(x-π/6)
所以y=sin(3x+π/3)cos(x-π/6)-cos(3x+π/3)sin(x-π/6)
=sin[(3x+π/3)-(x-π/6)]
=sin(2x+π/2)
=cos2x
cosx的对称轴用就是取最大或最小的地方,即x=kπ
所以此处是2x=kπ
x=kπ/2