令t=x-π/6,则原题变为limt趋向0 sin(-t)tan3(t+π/6)=-sint tan(3t+π/2)=sint cot3t,将cot3t放到分母，则变成sint/tan3t,sint等价于t，tan3t等价于3t，则变为t/3t,所以极限应该是1/3
