Phân tích các đa thức sau thành nhân tử: a) x2 - y2 - 2x + 2y b) 2x + 2y - x2 - xy c) 3a2 - 6ab + 3b2 - 12c2 d) x2 - 25 + y2 + 2xy e) a2 + 2ab + b2 - ac - bc f) x2 - 2x - 4y2 - 4y cảm ơn ạ

$a,$ $x^2-y^2-2x+2y$

$=\left(x+y\right)\left(x-y\right)+2\left(-x+y\right)$

$=\left(x+y\right)\left(x-y\right)-2\left(x-y\right)$

$=\left(x-y\right)\left(x+y-2\right)$

$b,$ $2x+2y-x^2-xy$

$=\left(2x+2y\right)+\left(-x^2-xy\right)$

$=2\left(x+y\right)-x\left(x+y\right)$

$=\left(x+y\right)\left(2-x\right)$

$c,$ $3a^2-6ab+3b^2-12c^2$

$=3a^2+3\left(-2ab\right)+3b^2+3\left(-4c^2\right)$

$=3\left(a^2-2ab+b^2-4c^2\right)$

$=3\left[a^2-2\left(a\right)\left(b\right)+b^2-4c^2\right]$

$=3\left(\left(a-b\right)^2-4c^2\right)$

$=3\left(\left(a-b\right)^2-\left(2c\right)^2\right)$

$=3\left(a-b+2c\right)\left(a-b-2c\right)$

$d,$ $x^2-25+y^2+2xy$

$=\left(x+y\right)^2-25$

$=\left(x+y\right)^2-5^2$

$=\left[\left(x+y\right)+5\right]\left[\left(x+y\right)-5\right]$

$=\left(x+y+5\right)\left(x+y-5\right)$

$e,$ $a^2+2ab+b^2-ac-bc$

$=\left(a+b\right)^2-c\left(a+b\right)$

$=\left(a+b\right)\left(a+b\right)-c\left(a+b\right)$

$=\left(a+b\right)\left[\left(a+b\right)-c\right]$

$=\left(a+b\right)\left(a+b-c\right)$

$f,$ $x^2-2x-4y^2-4y$

$=\left(x+2y\right)\left(x-2y\right)-2\left(x+2y\right)$

$=\left(x+2y\right)\left(x-2y-2\right)$