1,$\left\{\begin{matrix} x^{2}(y+1)=6y-2 & \\ x^{4}y^{2}+2x^{2}y^{2}+y(x^{2}+1)=12y^{2}-1 & \end{matrix}\right.$
2,$\left\{\begin{matrix} y=-x^{3}+3x+4 & \\ x=2y^{3}-6y-2 & \end{matrix}\right.$
3,$\left\{\begin{matrix} (1+x)(1+x^{2})(1+x^{4})=1+y^{7} & \\ (1+y)(1+y^{2})(1+y^{4})=1+x^{7} & \end{matrix}\right.$
4,$\left\{\begin{matrix} x^{2}y+y^{3}=x^{4}+x^{6} & \\ (x+2)\sqrt{y+1}=(x+1)^{2} & \end{matrix}\right.$
Bài 4
PT (1)$x^2(y-x^2)+y^3-(x^2)^3=0 \Leftrightarrow \begin{bmatrix} y=x^2 & \\ x^2+y^2+x^2y+y^4(*) & \end{bmatrix}$
(*) thì xét denta chứng minh vô nghiệm