[tex]-2x^5+8x^4=2x^4(4-x)[/tex]
[tex]2x^5-4x^4+x^3=x^3(2x^2-4x+1)=2x^3\Big(x+\cfrac{1}{\sqrt{2}}-1\Big)\Big(x-\cfrac{1}{\sqrt{2}}-1\Big)[/tex]
[tex]4x^5 - 2x^4 - 16x^3 + 8x^2=2x^4(2x-1)-8x^2(2x-1)=(2x-1)(2x^4-8x^2)\\=2x^2(2x-1)(x^2-4)=2x^2(2x-1)(x-2)(x+2)[/tex]