Rút gọn

Rút gọn :
(x+3)×(x²-3x+9)-x³.
(3x+y)×(9x²-3xy+y²)=y³-26x³.
X³+8y³-(x+2y)×(x²-2xy-4y²).
(2x-y)×(4x²+2xy+y²)+y³=7x³.