a) Ta có:
(2x2-3xy+y2)(x+y)
= x.(2x2-3xy+y2)+y.(2x2-3xy+y2)
= 2x3-3x2y+xy2+2x2y-3xy2+y3
= 2x3-x2y-2xy2+y3
b) Ta có:
(x-2)(x2-5x+1)-x(x2+11)
= x.(x2-5x+1)-2.(x2-5x+1)-x(x2+11)
= x3-5x2+x-2x2+10x-2-x3-11x
= -7x2-2
c) Ta có:
[(x2-2xy+2y2)(x+2y)-(x2+4y2)(x-y)]2xy
= [x.(x2-2xy+2y2)+2y.(x2-2xy+2y2)-x.(x2+4y2)+y.(x2+4y2)].2xy
= (x3-2x2y+2xy2+2x2y-4xy2+4y3-x3-4xy2+x2y+4y3).2xy
= (x2y-6xy2+8y3).2xy
= 2x3y2-12x2y3+16xy4