已知函数f(x)=cos^4x-2sinxcosx-sin^4x,求f(x)的最小正周期,求f(x)的单调区间,

问题描述:

已知函数f(x)=cos^4x-2sinxcosx-sin^4x,求f(x)的最小正周期,求f(x)的单调区间,

f(x)=(cos²x+sin²x)(cos²x-sin²x)-sin2x=cos2x-sin2x=-(√2)sin[2x-(π/4).即f(x)=-(√2)sin[2x-(π/4)].∴(1)T=π.(2)2kπ-(π/2)≤2x-(π/4)≤2kπ+(π/2).===>kπ-(π/8)≤x≤kπ+(3π/8).∴...