`x+y-2=0`
`b)` `N=x^3+x^2y-2x^2-xy^2+2xy+2y+2x-2-x^2y`
`<=>N=x^2 (x+y-2)-(x^2y+xy^2-2xy)+(2x+2y-2)`
`<=>N=x^2(x+y-2)-xy(x+y-2)+2(x+y-2)`
`<=>N=(x+y-2)(x^2-xy+2)`
`<=>N=0.(x^2-xy+2)=0`
Vậy $N=0$
$\\$
`c)` $P=x^4+2x^3y-2x^3+x^2y^2-2x^2y-x(x+y)+2x+3$
`<=>P=(x^4+x^3y-2x^3)+(x^3y+x^2y^2-2x^2y)-[x(x+y)-2x]+3`
`<=>P=x^3 (x+y-2)+x^2y (x+y-2)-x(x+y-2)+3`
`<=>P=(x+y-2)(x^3 +x^2y-x)+3`
`<=>P=0.(x^3 +x^2y-x)+3`
`<=>P=0+3=3`
Vậy $P=3$