\(\left\{{}\begin{matrix}x^2+xy-2y^2=0\\xy+3y^2+x=3\end{matrix}\right.\)

\(\left\{{}\begin{matrix}\dfrac{4x}{1+4x}=\sqrt{y}\\\dfrac{4y}{1+4y}=\sqrt{z}\\\dfrac{4z}{1+4z}=\sqrt{x}\end{matrix}\right.\)

\(4y^2=2+\sqrt{199-x^2-2x}\)

\(\left\{{}\begin{matrix}x^3+2xy^2+12y=0\\8y^2+x^2=12\end{matrix}\right.\)

\(\left\{{}\begin{matrix}x^3-y^3=3\left(x-y\right)\\x+y=-1\end{matrix}\right.\)