2/ Thực hiện phét tính
a) ( x – y ). ( $x^{2}$ + xy + $y^{2}$ )
b) ( x – 2 $y^{2}$ ) . ( $x^{2}$ + 2xy + 4 $y^{2}$ )
c) ( x – 1 ) . ( x – 2 ) . x
d) 3$xy^{3}$ . ( $x^{3}$ – 2x -6 )
2/ Thực hiện phét tính
a) ( x – y ). ( $x^{2}$ + xy + $y^{2}$ )
b) ( x – 2 $y^{2}$ ) . ( $x^{2}$ + 2xy + 4 $y^{2}$ )
c) ( x – 1 ) . ( x – 2 ) . x
d) 3$xy^{3}$ . ( $x^{3}$ – 2x -6 )
Đáp án:
`a)(x-y)(x^2+xy+y^2)`
`=x^3+x^2y+xy^2-x^2y-xy^2-y^3`
`=x^3-y^3`
`b)(x-2y^2)(x^2+2xy+4y^2)`
`=x^3+2x^2y+4xy^2-2x^2y^2-4xy^3-8y^3`
`c)(x-1)(x-2).x`
`=x(x^2-x-2x+2)`
`=x(x^2-3x+2)`
`=x^3-3x^2+2x.`
`d)3xy^3(x^3-2x-6)`
`=3.(x^4y^3-2x^2y^3-6xy^3)`
`=3x^4y^3-2x^2y^3-6xy^3.`