(1)y=sinx^4+cosx^4
=(sin²x+cos²x)²-2sin²xcos²x
=1-sin²2x/2
=1-(1-cos4x)/4
最小正周期是：T＝2π/4＝π/2
(2)y=sinx^2+2sinxcosx
=(1-cos2x)/2+sin2x
=(1+2sin2x-cos2x)/2
=[1+√5sin(2x+a)]/2 (tana=-1/2)
=>最小正周期是：T＝2π/2＝π.