`2xy + 3z + 6y + xz`

`= (2xy+xz)+(3z+6y)`

`=x(2y+z)+3(z+2y)`

`=(2y+z)(x+3)`

`1-8x+16x^2-y^2`

`= ( 16x^2 - 8x + 1 ) - y^2`

`= [ (4x)^2 - 2 . 4x . 1 + 1 ] - y^2`

`= (4x-1)^2 - y^2`

`= (4x-y-1).(4x+y-1)`

y ko có mũ 2 á cậu

`x^2 - 2x - 3 = 0`

`=> ( x^2 + x ) + ( -3x - 3 ) = 0`

`=> x . ( x + 1 ) - 3 . ( x + 1 ) = 0`

`=> ( x + 1 ) . ( x - 3 ) = 0`

`=> x+1 = 0` hoặc `x-3=0`

`=> x=-1` hoặc `x=3`

   Vậy `x in { -1; 3 }`