Đáp án:
$\begin{array}{l}
a)13 - 3\left| {x + 1,5} \right| = 1\\
\Leftrightarrow 3\left| {x + 1,5} \right| = 12\\
\Leftrightarrow \left| {x + 1,5} \right| = 4\\
\Leftrightarrow \left[ \begin{array}{l}
x + 1,5 = 4\\
x + 1,5 = - 4
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 2,5\\
x = - 5,5
\end{array} \right.\\
Vậy\,x = 2,5;x = - 5,5\\
b){3^{x - 2}} + {5.3^{x + 1}} = 408\\
\Leftrightarrow {3^{x - 2}} + {5.3^3}{.3^{x - 2}} = 408\\
\Leftrightarrow {3^{x - 2}}.\left( {1 + {{5.3}^3}} \right) = 408\\
\Leftrightarrow {3^{x - 2}}.136 = 408\\
\Leftrightarrow {3^{x - 2}} = 3\\
\Leftrightarrow x - 2 = 1\\
\Leftrightarrow x = 3\\
Vậy\,x = 3\\
c)Dkxd:x \ne - \dfrac{1}{2};x \ne \dfrac{2}{3}\\
\dfrac{{ - 7}}{{1 + 2x}} = \dfrac{5}{{2 - 3x}}\\
\Leftrightarrow - 7.\left( {2 - 3x} \right) = 5.\left( {1 + 2x} \right)\\
\Leftrightarrow - 14 + 21x = 5 + 10x\\
\Leftrightarrow 11x = 19\\
\Leftrightarrow x = \dfrac{{19}}{{11}}\left( {tmdk} \right)\\
Vậy\,x = \dfrac{{19}}{{11}}
\end{array}$
