令a=x²+3x原式=(a+3)(a-4)+6=a²-a-12+6=a²-a-6=(a+2)(a-3)=(x²+3x+2)(x²+3x-3)=(x+1)(x+2)(x²+3x-3)令a=x²-5x原式=a(a-2)-24=a²-2a-24=(a+4)(a-6)=(x²-5x+4)(x²-...