phân tích thành nt 1)2xy-x^2-y^2+9 2)X^2_x+(2x+1)(x-1) 3)(x+2)^2+2.x+2.(x-1)+(x-1)^2 4)2x^2+4x+2-8y^2 5)X^2+2x-y^2+1 6)X^2+2xy+2y^2+xy

1)

$2xy – x² – y² + 9$

$= -(x² – 2xy + y²) + 9$

$= 3² – (x – y)²$

$= (3 + x – y)(3 – x + y)$

2)

$x² – x + (2x + 1)(x – 1)$

$= x(x – 1) + (2x + 1)(x – 1)$

$= (x – 1)(x + 2x + 1)$

$= (x – 1)(3x + 1)$

3)

$(x + 2)² + 2(x + 2)(x – 1) + (x – 1)²$

$=(x + 2 + x – 1)²$

$= (2x + 1)²$

4) $2x² + 4x + 2 – 8y²$

$= 2(x² + 2x + 1 – 4y²)$

$= 2((x + 1)² – (2y)²)$

$= 2(x + 1 – 2y)(x + 1 + 2y)$

5)

$x² + 2x – y² + 1$

$= x² + 2x + 1 – y²$

$= (x + 1)² – y²$

$= (x + 1 – y)(x + 1 + y)$

6)

$x² + 2xy + 2y² + xy$

$= x² + xy + 2y² + 2xy$

$= x(x + y) + 2y(x + y)$

$= (x + 2y)(x + y)$