D
duylinh1811


1.
[tex]\left\{ \begin{array}{l} x^4-x^3y+x^2y^2=1 \\ x^3y-x^2+xy=-1 \end{array} \right.[/tex]
[tex]\left\{ \begin{array}{l} x^4-x^3y+x^2y^2=1 \\ x^3y-x^2+xy=-1 \end{array} \right.[/tex]