$x^3-2x^3+x$
$=-x^3+x$
$=x(1-x^2)$
$=x(1-x)(1+x)$
$2x^2+4x+2-y^2$
$=2(x^2+2x+1)-y^2$
$=(\sqrt{2})^2(x+1)^2-y^2$
$=(\sqrt{2}x+\sqrt{2}-y)(\sqrt{2}x+\sqrt{2}+y)$
Hoặc đề sai :
$x^3-2x^2+x=x(x^2-2x+1)=x(x-1)^2$
$2x^2+4x+2-2y^2$
$=2(x^2+2x+1-y^2)$
$=2[(x+1)^2-y^2]$
$=2(x+1-y)(x+1+y)$