y=-1/2cot(π/3-2x）=1/2cot(2x-π/3)
周期T=π/2
单调区间
kπ=<2x-π/3<=(k+1)π
即kπ/2+π/6<=x<=(k+1)π/2+π/6
单调区间(kπ/2+π/6,(k+1)π/2+π/6) k=1,2,3,.
单调递减