Hệ phương trình \(\left\{ \begin{array}{l} \frac{2}{x} + y = 3\\ \frac{1}{2} - 2y = 4 \end{array} \right.\).

* Hướng dẫn giải

Ta có: 

\(\begin{array}{l} \left\{ \begin{array}{l} \frac{2}{x} + y = 3\\ \frac{1}{x} - 2y = 4 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} \frac{2}{x} + y = 3\\ \frac{2}{x} - 4y = 8 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} 5y = - 5\\ \frac{1}{x} - 2y = 4 \end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l} y = - 1\\ \frac{1}{x} - 2.( - 1) = 4 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} y = - 1\\ \frac{1}{x} = 2 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} y = - 1\\ x = \frac{1}{2} \end{array} \right.\\ = > \frac{x}{y} = \frac{{\frac{1}{2}}}{{ - 1}} = - \frac{1}{2} \end{array}\)

Chọn đáp án C