Cho \(\left\{ - y = - = \right.\) có nghiệm nào dưới đây?

* Hướng dẫn giải

 \(\begin{array}{l}\,\,\left\{ \begin{array}{l}\dfrac{2}{3}x - y = 70\\\dfrac{1}{3}x - \dfrac{2}{3}y = 43\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}\dfrac{2}{3}x - y = 70\\\dfrac{2}{3}x - \dfrac{4}{3}y = 86\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}\dfrac{1}{3}y = - 16\\\dfrac{2}{3}x - y = 70\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}y = - 48\\\dfrac{2}{3}x + 48 = 70\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}y = - 48\\\dfrac{2}{3}x = 22\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}y = - 48\\x = 33\end{array} \right.\end{array}\)