f(x)=cos^4x-2sinxcosx-sin^4x=(cos^2x+sin^2x)(cos^2x-sin^2x)-sin2x=cos2x-sin2x=√2cos(2x+π/4)当cos(2x+π/4)=1时,f(x)max=√22x+π/4=2kπ2x=-π/4+2kπ{x|x=-π/8+kπ}2x+π/4=π/2+kπ2x=π/4+kπx=π/8+kπ...