1、y=(cos^2x+sin^2x)^2-2cos^2xsin^2x
=1-1/2(sin2x)^2
=1-1/4(1-cos4x)
=3/4+1/4cos4x
周期T=2pi/4=pi/2
2、y=(根3/2sin2x+1/2cos2x)/((根3/2cos2x-1/2sin2x)
=sin(2x+pi/6)/cos(2x+pi/6)
=tan(2x+pi/6)
T=pi/2
3、3y=3xin(2x+π/4)减区间
pi/2+2kpi