函数Y=cos(4)次方x-sin(4)次方xde最小正周期怎么求

cos^4x-sin^4x=(cos^2x)^2-(sin^2x)^2=(cos^2x+sin^2x)(cos^2x-sin^2x)
=1*(cosx+sinx)(cosx-sinx)
然后提一个根号2。。。很难打。。。你确定要看下去？？