(x+3)(ax^2+bx-2)=ax^3+bx^2-2x+3ax^2+3bx-6=ax^3+(3a+b)x^2+(3b-2)x+3bx 不含x^2项和x项所以 3a+b=0 3b-2=0 b=2/3 a=-2/9