Đáp án: $\,a = - 8;b = - 12;c = - 15$
Giải thích các bước giải:
$\begin{array}{l}
\dfrac{a}{2} = \dfrac{b}{3};\dfrac{b}{4} = \dfrac{c}{5}\\
\Leftrightarrow \left\{ \begin{array}{l}
\dfrac{a}{{2.4}} = \dfrac{b}{{3.4}}\\
\dfrac{b}{{3.4}} = \dfrac{c}{{3.5}}
\end{array} \right.\\
\Leftrightarrow \dfrac{a}{8} = \dfrac{b}{{12}} = \dfrac{c}{{15}} = \dfrac{{2c}}{{30}} = \dfrac{{a + b - 2c}}{{8 + 12 - 30}} = \dfrac{{10}}{{ - 10}} = - 1\\
\Leftrightarrow \left\{ \begin{array}{l}
a = - 8\\
b = - 12\\
c = - 15
\end{array} \right.\\
Vậy\,a = - 8;b = - 12;c = - 15
\end{array}$
