x→0lim x^2 / sin^2(x/3)=lim 9*x^2/9 / sin^2(x/3)=9*lim (x/3)^2 / sin^2(x/3)=9*lim [(x/3) / sin(x/3)]^2=9*[lim (x/3) / sin(x/3)]^2根据重要的极限：lim sinx/x=1=9*1^2=9有不懂欢迎追问
