Giải thích các bước giải:
\(\begin{array}{l}
\left\{ \begin{array}{l}
y = a - 2ax\\
3ax - \left( {a - 1} \right)\left( {a - 2ax} \right) = 2a
\end{array} \right.\\
\Rightarrow 3ax + 2a\left( {a - 1} \right)x - a\left( {a - 1} \right) = 2a\\
\Leftrightarrow x\left( {2{a^2} + a} \right) = {a^2} + a\\
\Rightarrow x = \dfrac{{a + 1}}{{2a + 1}}\left( {a \ne 0;a \ne - \dfrac{1}{2}} \right)\\
\Rightarrow y = a - 2a.\dfrac{{a + 1}}{{2a + 1}} = \dfrac{{2{a^2} + a - 2{a^2} - 2a}}{{2a + 1}} = \dfrac{{ - a}}{{2a + 1}}\\
2x - y = 2.\dfrac{{a + 1}}{{2a + 1}} - \dfrac{{ - a}}{{2a + 1}}\\
= \dfrac{{3a + 2}}{{2a + 1}} > 0\\
\Leftrightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
3a + 2 > 0\\
2a + 1 > 0
\end{array} \right.\\
\left\{ \begin{array}{l}
3a + 2 < 0\\
2a + 1 < 0
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
a > - \dfrac{2}{3}\\
a > \dfrac{{ - 1}}{2}
\end{array} \right.\\
\left\{ \begin{array}{l}
a < \dfrac{{ - 2}}{3}\\
a < - \dfrac{1}{2}
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
a > \dfrac{{ - 1}}{2}\\
a < - \dfrac{2}{3}
\end{array} \right.
\end{array}\)
