f(x)=2sinxcos(π/6)+cosx
=√3sinx+cosx
=2sin(x+π/6)
周期为2π
2kπ+π/2≤x+π/6≤2kπ+3π/2,k∈Z.
解得2kπ+π/3≤x≤2kπ+4π/3
在[0,2π]上的单调递减区间是[π/3,4π/3]