原式＝(x^2+x-2)(x^2+7x+12)-24＝(x^4+7x^3+12x^2+x^3+7x^2+12x-2x^2-14x-24)+24＝x^4+8x^3+17x^2-2x＝x(x^3+8x^2+17x-2)
