Đáp án:
$\begin{array}{l}
\frac{{7{x^2} - 14x - 5}}{{15}} = \frac{{{{\left( {2x + 1} \right)}^2}}}{5} - \frac{{{{\left( {x - 1} \right)}^2}}}{3}\\
\Rightarrow \frac{{7{x^2} - 14x - 5}}{{15}} = \frac{{3\left( {4{x^2} + 4x + 1} \right) - 5\left( {{x^2} - 2x + 1} \right)}}{{15}}\\
\Rightarrow \frac{{7{x^2} - 14x - 5}}{{15}} = \frac{{7{x^2} + 22x - 2}}{{15}}\\
\Rightarrow 7{x^2} - 14x - 5 = 7{x^2} + 22x - 2\\
\Rightarrow 36x = - 3\\
\Rightarrow x = - \frac{1}{{12}}
\end{array}$
