Suoyi a<0 has nothing to do with B.

2. Let 3x+2y+z=5 be A, x+y-z=2 be B, then A-B=2x+y-2z=3, then

2x+y-z=3+z, that is, s=3+z, z>0, so s> three.

3, by ax+b & gt；; 0，x & lt 1/3-a & lt； 0, b<0, b/a= 1/3, so bx-a.