Hệ \(\left\{ \begin{array}{l}2x + 18y = - 9\\4x + 18y = - 27\end{array} \right.\) có nghiệm (m, n). Tính m : n.

* Hướng dẫn giải

 \(\begin{array}{l}\,\,\left\{ \begin{array}{l}2x + 18y = - 9\\4x + 18y = - 27\end{array} \right. \\ \Leftrightarrow \left\{ \begin{array}{l}2x = - 18\\2x + 18y = - 9\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}x = - 9\\2.\left( { - 9} \right) + 18y = - 9\end{array} \right. \\ \Leftrightarrow \left\{ \begin{array}{l}x = - 9\\18y = 9\end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l}x = - 9\\y = \dfrac{1}{2}\end{array} \right.\end{array}\)

⇒ m : n = -18