Lấy \(PT\left(2\right)-PT\left(1\right)\) ta được :
\(x^4+y^2+2x^2y-x^2-y-x^3y-xy^2=0\)
\(\Leftrightarrow\left(x^2+y\right)^2-\left(x^2+y\right)-xy\left(x^2+y\right)=0\)
\(\Leftrightarrow\left(x^2+y\right)\left(x^2+y-xy-1\right)=0\)
\(\Leftrightarrow\left(x^2+y\right)\left[\left(x-1\right)\left(x+1\right)-y\left(x-1\right)\right]=0\)
\(\Leftrightarrow\left(x^2+y\right)\left(x-y+1\right)\left(x-1\right)=0\)
Xét các TH xong thay vô