Đáp án + Giải thích các bước giải:
1) $2x^2 + xy -3y^2 -x+y\\=(2x^2-2xy)+(-3y^2+3xy)-(x-y)\\=2x(x-y)+3y(-y+x)-(x-y)\\=2x(x-y)+3y(x-y)-(x-y)\\=(x-y)(2x+3y-1)$
2) $x^2+xy - 2y^2 + 2x- 2y \\=(x^2+2xy)-(2y^2+xy)+(2x-2y)\\=x(x+2y)-y(x+2y)+2(x-y)\\=(x+2y)(x-y)+2(x-y)\\=(x-y)(x+2y+2)$
4) $x^2 + y^2 - 4z^2 + 2xy - 4z -1\\=(x^2+2xy+y^2)-(4z^2+4z+1)\\=(x+y)^2-(2z+1)^2\\=(x+y+2z+1)(x+y-2z-1)$