Tìm x, biết: ​\( \frac{{ - 2}}{x} = \frac{{ - x}}{{\frac{8}{{25}}}}\)

* Hướng dẫn giải

 \(\begin{array}{l} \frac{{ - 2}}{x} = \frac{{ - x}}{{\frac{8}{{25}}}} \Rightarrow - 2.\frac{8}{{25}} = x.\left( { - x} \right)\\ \Rightarrow - \frac{{16}}{{25}} = - {x^2} \Rightarrow {x^2} = \frac{{16}}{{25}}\\ \Rightarrow {x^2} = {\left( {\frac{4}{5}} \right)^2} \to \left[ \begin{array}{l} x = \frac{4}{5}\\ x = - \frac{4}{5} \end{array} \right. \end{array}\)