Ta có: `P= x^3 + x^2y - 2x^2 - xy - y^2 + 3y + x + 2017`
`P= (x^3 + x^2y - 2x^2) - ( xy + y^2 - 3y) + x+2017`
`P= x^2(x + y - 2) - y(x+y-3) + x+2017`
`P= x^2( 2-2) - y(2 -3) + x+2017`
`P= x^2 .0 + y + x + 2017`
`P = y + x + 2017`
Mà `y+x =2`
`=> P =2+2017`
`=> P= 2019`
Vậy `P= 2019` khi `x+y=2`