x^5-1
=x^5-x^2+x^2-1
=x^2(x^3-1)+(x+1)(x-1)
=x^2(x-1)(x^2+x+1)+(x+1)(x-1)
=(x-1)(x^4+x^3+x^2)+(x+1)(x-1)
=(x-1)(x^4+x^3+x^2+x+1)
也可以直接运用五次方公式,即
a^5-1=(a-1)(a^4+a^3+a^2+a+1)