4x^3-x =x(4x²-1)=x(2x-1)(2x+1) （x+y）^2-9x^2=(x+y-3x)(x+y+3x)=(y-2x)(y+4x) x^2-y^2+2（x-y）=(x-y)(x+y)+2(x-y)=(x-y)(x+y+2) 8（x^2-2y^2）-x（7x+y）+xy、=8x²-16y²-7x²-xy+xy=x²-16y²=(x-4y)(x+4y)
