a)(2x-1)^2-(4x+1)(x-3)=-3 b) cho x+y+z=0.Chứng minh rằng x^3+y^3+z^3=3xyz

`a) => 4x^2-4x+1-4x^2+11x+3=-3`

`=> 7x+4=-3`

`=> 7x=-3-4=-7`

`=> x=-1`

`b) x+y+z= 0`
`=> x+y=-z`
`=> (x+y)^3 =-z^3`
`=> x^3 +y^3 +3xy(x+y) =-z^3`
`=> x^3 +y^3 +3xy(-z) =-z^3`
`=> x^3 +y^3 -3xyz =-z^3`
`=> x^3 +y^3 + z^3 =3xyz  ( đpcm )`