(1/2x+π/3)-(1/2x-π/6)=π/2,
∴cos(1/2x-π/6)=cos[(1/2x+π/3)-π/2]=-sin(1/2x+π/3)
即y=sin(1/2x+π/3)-cos(1/2x-π/6)+7
=2sin(1/2x+π/3)+7
函数的周期T=2π/(1/2)=4π