y=1/2sin(2x+π/3)-sinxcosx=1/2(1/2sin2x+√3/2cos2x)-1/2sin2x=1/2(-1/2sin2x+√3/2cos2x)=1/2(cosπ/6cos2x-sinπ/6sin2x)=1/2cos(2x+π/6)当2x+π/6∈[0+2kπ,π+2kπ](k∈Z)时,y单调递减即0+2kπ≤2x+π/6≤π+...