(x1-x2)+(a/x1-a/x2)为什么能等于(x1-x2)(1-a/x1x2)求过程

(x1-x2)+(a/x1-a/x2)
==> x1-x2+a/x1-a/x2
==>x1- x2 + x2*a/x1*x2 - x1*a/x1*x2
==>(x1-x2) - (x1-x2)*a/x1*x2
==>(x1-x2)(1-a/x1x2)

(x1-x2)+(a/x1-a/x2)
=(x1-x2)+a(x2-x1)/x1x2
=(x1-x2)-a(x1-x2)/x1x2
=(x1-x2)[1-a/x1x2]
若还有疑问就HI我啦.