6.
$= (2x)^2 - 5^2$
$= 4x^2 - 25$
7.
$= 8x^3 + 3 . 4x^2y^2 + 3 . 2xy^4 + y^6$
$= 8x^3 + 12x^2y^2 + 6xy^4 + y^6$
8.
$= x^3 + 3x^2 . 3 + 3x . 3^2 + 3^3$
$= x^3 + 9x^2 + 27x + 27$
9.
$= (2/3x^2) - 3 . (2/3x^2)^2 . 1/2y + 3 . 2/3x^2 . (1/2y)^2 - (1/2y)^3$ $= 8/27x^6 - 2/3x^4y + 1/2x^2y^2 - 1/8y^3$
10.
$= (3x^2)^3 - 3. (3x^2)^2 . 2y + 3 . 3x^2 . (2y)^2 - (2y)^3$
$= 27x^6 - 54x^4y + 36x^2y^2 - 8y^3$
Xinhaynhat
