y=sin(1/2x+π/3),x属于R
当1/2x+π/3=2kπ+π/2时,y=sin(1/2x+π/3)有最大值1
此时x=4kπ+π-2π/3=4kπ+π/3,k∈Z
当1/2x+π/3∈【2kπ+π/2,2kπ+3π/2）时y单调减
此时：x∈【4kπ+π/3,(4k+2)π+π/3),其中k∈Z