Dễ thấy x,y khác 0
\(\left\{{}\begin{matrix}2x^2+y^2=12\\xy=-4\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}2x^2+\left(-\frac{4}{x}\right)^2=12\\y=-\frac{4}{x}\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}2x^2+\frac{16}{x^2}=12\\y=-\frac{4}{x}\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}2x^4-12x^2+16=0\\y=-\frac{4}{x}\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}2\left(x^2-2\right)\left(x^2-4\right)=0\\y=-\frac{4}{x}\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}\left[{}\begin{matrix}x^2=2\\x^2=4\end{matrix}\right.\\y=-\frac{4}{x}\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=\sqrt{2}\Rightarrow y=-2\sqrt{2}\\x=-\sqrt{2}\Rightarrow x=2\sqrt{2}\\x=2\Rightarrow y=-2\\x=-2\Rightarrow y=2\end{matrix}\right.\)
