y=√3sin(2x)+cos(2x)
=2[sin(2x)(√3/2)+cos(2x)(1/2)]
=2sin(2x+π/6)
x∈（-π,0）
2x+π/6∈(-11π/6,π/6)
sin(2x+π/6)单调递减区间为[-3π/2,-π/2],此时
-3π/2≤2x+π/6≤-π/2
-5π/6≤x≤-π/3
函数的单调递减区间为[-5π/6,-π/3]