f(x)=sinxcosπ/6+cosxsinπ/6+2sinxcosπ/6-cosxsinπ/6+cosx+a=2sinxcosπ/6+cosx+a=√3sinx+cosx+a=2sin(x+π/6)+a最大值=2+a=1a=-1f(x)=2sin(x+π/6)-1>=0sin(x+π/6)>=1/2=sinπ/6=sin5π/6所以2kπ+π/6