=x^3 -8y^3 -2(x-2y)
=(x-2y)(x^2 +2xy +4y^2)- 2(x-2y)
=(x-2y)(x^2+2x +4y^2-2)
k day nhe
Ta co: x3 - 2x + 4y -8y3 = (x3 -8y3) -(2x -4y) = (x - 2y)(x2 + 2xy +y2) -2(x-2y) = (x-2y)(x2 + 2xy + y2 -2)
x3 - 2x + 4y - 8y3
= ( x3 - 8y3 ) - ( 2x - 4y )
= ( x - 2y )( x2 + 2xy + 4y2 ) - 2( x - 2y )
= ( x - 2y )( x2 + 2xy + 4y2 - 2 )