1. -(x^2-7x+12)=-(x-3)(x-4)2. -(2x^2-5x-3)=-(2x+1)(x-3)
（1）原式=-(x²-7x+12)=-（x-3)(x-4)(2)原式=-(2x²-5x-3）=-(2x+1)(x-3)
