x³+x²y-x²z-xyz
=x²(x+y)-xz(x+y)
=(x²-xz)(x+y)
=x(x-z)(x+y)
9（x²-y²）-（y-x）²
=9(x+y)(x-y)-(y-x)²
=(x-y)(9x+9y-x+y)
=2(x-y)(4x-5y)
x^m-1 -x^m+2 +x^m -x^m+1
=x^m-1(1-x³+x-x²)
=x^m-1[(1+x)-x²(1+x)]
=x^m-1(1-x²)(1+x)
=x^m-1(1-x)(1+x)²