`a)VT=(x+y+z)^3 `
`=[(x+y)+z]^3`
`=(x+y)^3+3z(x+y)^2+3z^2(x+y)+z^3`
`=x^3+3x^2y+3xy^2+y^3+3z(x+y)^2+3z^2(x+y)+z^3`
`=x^3+y^3+z^3+3xy(x+y)+3z(x+y)^2+3z^2(x+y)`
`=x^3+y^3+z^3+3(x+y)[xy+z(x+y)+z^2]`
`=x^3+y^3+z^3+3(x+y)(xy+zx+zy+z^2)`
`=x^3+y^3+z^3+3(x+y)[x(y+z)+z(y+z)]`
`=x^3+y^3+z^3+3(x+y)(y+z)(x+z)=VP`
`b)``( 8y^ ² - y +1)(y + 1) + y ^² ( 4- 3y) = -5/2 `
`<=> 8y^3+7y^2+1+ 4y ^² - 3y^3 +5/2=0 `
`<=> 12y^3+4y^2+ 7/2=0 `
`<=> 4y^2(3y+1)=- 7/2 `
`<=> y^2(3y+1)=- 7/16 `
Bn xem lại đề nhé
`---text(@ Ngọc Châu)---`