\(\begin{array}{l}
Ta\,\,co:\\
- \frac{{15}}{{5,1}} = \frac{{50}}{{17}}\\
- \frac{{35}}{{11,9}} = - \frac{{50}}{{17}}\\
\Rightarrow Ti\,\,\,le\,\,\,thuc: - \frac{{15}}{{5,1}} = - \frac{{35}}{{11,9}}\,\,\,\left( { - \frac{{50}}{{17}}} \right).\\
\frac{{2,1}}{7} = \frac{{21}}{{70}} = \frac{3}{{10}}\\
\Rightarrow Ti\,\,\,le\,\,\,thuc:\,\,\,\frac{{2,1}}{7} = \frac{3}{{10}}.
\end{array}\)