giúp mình làm bài hộ

`#0409`

Bài `1`

`a,` `(x+1)(x+5)=x(x+5)+1(x+5)=x^2+6x+5`

`b,` `(x+2)(x-7)=x(x-7)+2(x-7)=x^2-5x-14`

`c,` `(x-8)(2x+1)=x(2x+1)-8(2x+1)=2x^2-15x-8`

`d,` `(x-1)(x+1)(x-2)=(x^2-1)(x-2)=x^3-2x^2-x+2`

`e,` `(4x-6)(2x+3)=2(2x-3)(2x+3)=2(4x^2-9)=8x^2-18`

Bài `2`

`a,` `(2x+3y)(x-y)=2x(x-y)+3y(x-y)=2x^2+xy-3y^2`

`b,` `(x+2y)(x^2-2xy+4y^2)-x^3+(2y)^3=x^3+8y^3`

`c,` `(5x-3y)(25x^2+15xy+9y^2)=(5x)^3-(3y)^3=125x^3-27y^3`

`d,` `(-2x . 1/3y^2+2/3y^2+4xy^3) . 3/2xy=-2/3xy^2 . 3/2xy+2/3y^2 . 3/2xy+4xy^3 . 3/2xy=-x^2y^3+xy^3+6x^2y^4`

`e,` `-1/3xy . (3x^3y^3+6x^2y-4xy^2)=-1/3xy . 3x^3y^3-1/3xy . 6x^2y+1/3xy . 4xy^2=-x^4y^4-2x^3y^2+4/3x^2y^3`