首先把x^(-2/3)提取出来y=1/3*x^(-2/3)*(1+(1-2/3(x-1)x^(-1))=1/3*x^(-2/3)*(1+(1-2/3(1-x^(-1))=1/3*x^(-2/3)*(1+1-2/3+2/3x^(-1))=1/3*x^(-2/3)*(4/3+2/3x^(-1)) 最后一个括号里通分=1/3*x^(-2/3)*((4x+2)/3x)= (4x+2)/(9x*x^(-2/3)) 即是答案