y=sinxcos(x+π／6)-1/2cos2x
=[sinx(√3cosx-sinx)/2]-(cos2x)/2
=(√3sin2x-2sin²x-2cos2x)/4²
=(√3sin2x-cos2x-1)/4
=[2sin(2x+π/6)-1]/4
函数的最大值1/4
2x+π/6=(2n+1/2)π
x=(n+1/6)π