ac-bc+a·a-ab=c(a-b)+a(a-b)=(a+c)(a-b)a-b=3b+c=-5两式相加，a+c=-2所以原式=-2*3=-6
ac-bc+a·a-ab=c(a-b)+a(a-b)=(c+a)(a-b)=-2*3=-6
ac-bc+a·a-ab = c(a-b) + a(a-b) = (c+a)(a-b) = (a-b+b+c)(a-b) = (-2)(3) = -6
