y=sin^4 x+cos^2 x
=(sin^2 x)^2+cos^2 x
=[(1-cos2x)^2]/4+(1+cos2x)/2
=(1+cos^2 2x-2*cos2x)/4+(2+2*cos2x)/4
=(3+cos^2 2x)/4
=[3/4+1/4*(1+cos4x)/2]
=1/8*cos4x+7/8
则T=2兀/4=兀/2