f(x) = 2√3sinxcosx + 2cos^2x-1
= √3sin2x + cos2x
= 2(sin2xcosπ/6+cos2xsinπ/6)
= 2sin(2x+π/6)
2x+π/6 ∈（2kπ+π/2,2kπ+3π/2）时,单调减
∴单调递减区间（kπ+π/6,kπ+2π/3）