x^5-x^4+x^3-x^2+x-1
=x^4(x-1)+x^2(x-1)+(x-1)
=(x-1)(x^4+x^2+1)
=(x-1)(x^4+2x^2+1-x^2)
=(x-1)[(x^2+1)^2-x^2]
=(x-1)(x^2+1+x)(x^2+1-x)