Đáp án:
$1) 3x^2 -6x =3x(x-2)$
$2) 15x^2y -9x^2y^2 = 3x^2y(5-3y)$
$3) 2x^2(x-3)-x.(x-3)= (x-3)(2x^2-x)= x(2x-1)(x-3)$
$4)25x^2 -10xy +y^2 =(5x-y)^2 = (5x-y)(5x-y)$
$5)4y^2 +4y+1 = (2y+1)^2 = (2y+1)(2y+1)$
$8) x^3 -x+y^3 -y$
$=(x^3+y^3)-(x+y)$
$=(x+y)(x^2+xy+y^2)-(x+y)$
$=(x+y)(x^2+xy+y^2-1)$
$9) x^2-2xy-4z^2+y^2$
$=(x^2-2xy+y^2)-4z^2$
$=(x-y)^2 -4z^2$
$=(x-y+2z)(x-y-2z)$
$10) x.(x-1)-y(1-x)$
$=x(x-1) +y(x-1)$
$=(x-1)(x+y)$
$11) x^2-xy+x-y$
$=x(x-y)+(x-y)$
$=(x-y)(x+1)$
$12) xz +yz -5x-5y$
$=z(x+y)-5(x+y)$
$=(x+y)(z-5)$
