原式=
6x^3-6x^2-(5x^2-x-4)
=6x^2(x-1)-(5x+4)(x-1)
=(6x^2-5x-4)(x-1)
=(2x+1)(3x-4)(x-1)
2.由（2）式得x小于1
由（1）式得x大于a. 所以x取0,-1,-2
所以a的取值范围为a大于-3,小于等于-2.