f(x)=sin^2x-cosxsinx
f(x)=(1-cos2x-sin2x)/2
f(x)=(1-(cos2x+sin2x))/2
f(x)=(1-2^(1/2)sin(2x+45度))/2
max=(1+2^(1/2)*1)/2
=(1+2^(1/2))/2