banj lam giup minh nha , minh se vote 5 sao

Giải thích các bước giải:

a.Ta có:

$P=x^2-xy-x+xy^2-y^3-y^2+5$

$\to P=(x^2-xy)-x+(xy^2-y^3)-y^2+5$

$\to P=x(x-y)-x+y^2(x-y)-y^2+5$

$\to P=x-x+y^2-y^2+5$ vì $x-y=1$

$\to P=5$

b.Ta có:

$Q=x^3-x^2y-x^2+xy^2-y^3-y^2+5x-5y-2012$

$\to Q=(x^3-x^2y)-x^2+(xy^2-y^3)-y^2+(5x-5y)-2012$

$\to Q=x^2(x-y)-x^2+y^2(x-y)-y^2+5(x-y)-2012$

$\to Q=x^2-x^2+y^2-y^2+5-2012$ vì $x-y=1$

$\to Q=-2007$