图
x^5-x^3+x^2-1＝(x^5+x^2)-(x^3+1)=x^2(x^3+1)-(x^3+1)=(x^3+1)(x^2-1)=(x+1)(x^2-x+1)(x+1)(x-1)=(x+1)^2(x^2-x+1)(x-1)
x5-x3+x2-1=x³（x²-1）+（x²-1）=（x²-1）（x³+1）=（x+1）²（x-1）（x²-x+1）
=4X-1=(2X+1)(2X-1)
