约分,(x-y)(a-b)/(x^2-y^2)(b-a)
问题描述：
约分,(x-y)(a-b)/(x^2-y^2)(b-a)
答
(x-y)(a-b)
___________
(x2-y2)(b-a)
=-(x-y)(b-a)
___________
(x-y)(x+y)(b-a)
= -1
____
(x+y)