a=1,b=2或a=-1.b=-2.该题应给出基本变量x的变化趋势x→1,a/(1-x)-b/(1-x^2)=(ax+(a-b))/(1-x^2)当x→1时,1-x^2→0,1-x^2=(1-x)*(1+x)欲使极限存在必须ax+(a-b)=x-1,或者ax+(a-b)=1-x由ax+(a-b)=x-1和x的任意性得a=1,...