f(x)=(sin^2x+cos^2x)(sin^4x-sin^2x*cos^2x+cos^4x)=sin^4x-sin^2x*cos^2x+cos^4x=(sin^2x+cos^2x)^2-3sin^2x*cos^2x=1-3/4*(4sinx*cosx)^2=1-(3/4)sin^2 2x=1-(3/4)(1-cos4x)/2=5/8+(3/8)cos4x最小周期T=2π/4=π/2
