\(\Leftrightarrow\left\{{}\begin{matrix}x^2+4y^2-4xy=2-4xy\\\left(x-2y\right)\left(1-2xy\right)=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}\left(x-2y\right)^2=2\left(1-2xy\right)\\\left(x-2y\right)\left(1-2xy\right)=4\end{matrix}\right.\)
Đặt \(\left\{{}\begin{matrix}x-2y=a\\1-2xy=b\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a^2=2b\\ab=4\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a^2=2b\\a.\frac{a^2}{2}=4\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}b=\frac{a^2}{2}\\a^3=8\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}a=2\\b=2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}x-2y=2\\1-2xy=2\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}x=2y+2\\1-2y\left(2y+2\right)=2\end{matrix}\right.\) (casio pt dưới)
