y=cos^2（x）-sinxcosx-3sin^2（x）的最大值

y=1-(1/2)sin2x-4(sinx)^2=1-(1/2)sin2x+2(cos2x-1)=-1+2cos2x-(1/2)sin2x√[2^2+(1/2)^2]=√17/2sinu=2/(√17/2) cosu=(1/2)/(√17/2)y=-1+(√17/2)*sin(u-2x)90>=x>=0u>=u-2x>=0y最大=-1+(√17/2)...