2.B=(X−2Y)¡X2+2X Y+4Y2¢−2Y(X−2Y)(X+2Y).#VÍ DỤ 3. CHO X=−3

2.B=(x−2y)¡x

2

+2x y+4y

2

¢−2y(x−2y)(x+2y).#Ví dụ 3. Cho x=−3