\(\begin{array}{l}
5)\frac{a}{{b + c}} = \frac{b}{{a + c}} = \dfrac{c}{{a + b}} = \dfrac{{a + b + c}}{{2\left( {a + b + c} \right)}} = \dfrac{1}{2}\\
\Rightarrow \left\{ \begin{array}{l}
2a = b + c\\
2b = a + c\\
2c = a + b
\end{array} \right. \Rightarrow a = b = c
\end{array}\)