Giải thích các bước giải:
$\begin{array}{l}
G/s:\,\frac{a}{b} = \frac{c}{d} = k \Rightarrow a = b.k;c = d.k\\
\frac{{15a + 7b}}{{15a - 7b}} = \frac{{15.b.k + 7b}}{{15.b.k - 7b}} = \frac{{15k + 7}}{{15k - 7}}\\
\frac{{15c + 7d}}{{15c - 7d}} = \frac{{15.d.k + 7d}}{{15d.k - 7d}} = \frac{{15k + 7}}{{15 - 7}}\\
\Rightarrow \frac{{15a + 7b}}{{15a - 7b}} = \frac{{15c + 7d}}{{15c - 7d}}\left( { = \frac{{15k + 7}}{{15 - 7}}} \right)
\end{array}$
