(1/x三次-1/x平方)*x平方/x-1
=(1/x^3-1/x^2)*x^2/(x-1)
=(x^2/x^3-x^2/X^2)/(x-1)
=(1/x-1)/(x-1)
=(1-x)/(x(x(x-1))
=-1/x
第二道题分母再多加个括号,分不清哪些是分母.