x³-4x²y＝x²(x-4y)x的四次方-5x²+4=(x²-4)(x²-1)=(x+2)(x-2)(x+1)(x-1)6x²+7x-5 =(2x-1)(3x+5)5x-5x³=5x(1-x²)=5(1+x)(1-x)