f(x)=cos(2pai-x)cos(pai/2-x)-sin^2x=cosxsinx-sin²x=(1/2)sin2x-(1-cos2x)/2=(1/2)(sin2x+cos2x)-1/2=(√2/2)sin(2x+π/4)-1/2最小正周期为 2π/2=π当 2x+π/4∈[2kπ-π/2,2kπ+π...