①x²-x-6=(x-3)(x+2)
②x²+x-12=(x+4)(x-3)
③-x²-5x-4=-(x+4)(x+1)
④x²+3xy-28y²=(x+7y)(x-4y)
⑤（a+b）²-4（a+b）-12=(a+b-6)(a+b+2)
⑥（x²-x）²-4
=(x²-x-2)(x²-x+2)
=(x-2)(x+1)(x+2)(x-1)