Đáp án+Giải thích các bước giải:

 `a)x^{2}-y^{2}-2x+2y`

`=(x^{2}-y^{2})-2.(x-y)`

`=(x-y).(x+y)-2.(x-y)`

`=(x-y).(x+y-2)`

`b)2x+2y-x^{2}-xy=2.(x+y)-x.(x+y)=(2-x).(x+y)`

`c)3a^{2}-6ab+3b^{2}-12c^{2}=3.[(a^{2}-2.a.b+b^{2}-4c^{2}]`

`=3.[(a-b)^{2}-(2c)^{2}]=3.(a-b-2c).(a-b+2c)`

`d)x^{2}-25+y^{2}+2xy=(x^{2}+2.x.y+y^{2})-25=(x+y)^{2}-5^{2}=(x+y-5).(x+y+5)`

`e)a^{2}+2ab+b^{2}-ac-bc=(a^{2}+2.a.b+b^{2})-c.(a+b)=(a+b)^{2}-c.(a+b)=(a+b).(a+b-c)`

`f)x^{2}-2x-4y^{2}-4y=[x^{2}-(2y)^{2}]-2.(x+2y)=(x-2y).(x+2y)-2.(x+2y)=(x+2y).(x-2y-2)`

`g)x^{2}y-x^{3}-9y+9x=x^{2}.(y-x)-9.(y-x)=(y-x).(x^{2}-3^{2})=(y-x).(x-3).(x+3)`

`h)x^{2}.(x-1)+16.(1-x)=x^{2}.(x-1)-16.(x-1)=(x-1).(x^{2}-4^{2})=(x-1).(x-4).(x+4)`