a+b+c=0.所以b+c=-a a+b=-c a+c=-b 题目写错了,应该是 a(b/1+c/1)+c(a/1+b/1)+b(a/1+c/1) a(b/1+c/1)+c(a/1+b/1)+b(a/1+c/1) =b/a+c/a+a/c+b/c+a/b+c/b =b/(a+c)+c/(a+b)+a/(b+c) =b/(-b)+c/(-c)+a/(-a) =-1-1-1 =-3