$a.x^{2}(1-x^2)-4-4x^2$
$=x^{2}-x^4-4x^2-4$
$=x^{2}-(x^4+4x^2+4)$
$=x^{2}-(x^2$=(x^{}-x^2-2)(x+x^2+2)$ +2)^2$
$b.x^{2}+y^2-x^2y^2+xy-x-y$
$=x^{2}-x^2y^2+y^2-y+xy-x$
$=x^{2}(1-y^2)+y(y-1)+x(y-1)$
$=x^{2}(1-y)(1+y)+(y-1)(x+y)$
$=x^{2}(1-y)(1+y)-(1-y)(x+y)$
$=(y-1)^{}(x+y-x^2-x^2y)$
$=^{}(y-1)[y(1-x^2)+x(1-x)]$
$=^{}(y-1)(1-x)(y+xy+x)$
Chúc bạn học tốt !!!!
