Giải thích các bước giải:
$a.x^2(x-y)-(x-y)=(x^2-1)(x-y)=(x-1)(x+1)(x-y)$
$\begin{split}b.y^2-x^2-6x-9&=y^2-(x^2+6x+9)\\&=y^2-(x+3)^2\\&=(y-x-3)(y+x+3)\end{split}$
$c.x(x-2)+x-2=(x+1)(x-2)$
$\begin{split}d.x^2-y^2-2y-1&=x^2-(y^2+2y+1)\\&=x^2-(y+1)^2\\&=(x-y-1)(x+y+1)\end{split}$
$e.8x-16-x^2=-(x^2-8x+16)=-(x-4)^2$