已知a+2B,c+5a?是a+2B=0,c+5a=0吧?a+2b=0,a=-2b,b/a=-1/2c+5a=0,c=-5a,c/a=-5(6a+2b-c)/(a-4b+c) (分式上下同时除以a)=[6+2(b/a)-(c/a)]/[1-4(b/a)+(c/a)] =[6+2(-1/2)-(-5)]/[1-4(-1/2)+(-5)]=-5