a²-ab+ac-bc=0
a(a-b)+c(a-b)=0
(a-b)(a+c)=0
因为a≠b,所以a-b≠0
所以a+c=0
a=-c
a²-bc/a²+ac=a²-bc/(-c)²+a*(-a)
=a²-b/c-a²
=-b/c
=b/a