Đáp án:
$\begin{array}{l}
a){4^{x + 3}} - {3.4^{x + 1}} = {13.4^{11}}\\
\Leftrightarrow {4^{x + 1}}\left( {{4^2} - 3} \right) = {13.4^{11}}\\
\Leftrightarrow {4^{x + 1}}.13 = {13.4^{11}}\\
\Leftrightarrow {4^{x + 1}} = {4^{11}}\\
\Leftrightarrow x + 1 = 11\\
\Leftrightarrow x = 10\\
Vậy\,x = 10\\
b){2.3^{x + 2}} + {4.3^{x + 1}} = {10.3^6}\\
\Leftrightarrow {2.3^{x + 1}}\left( {3 + 2} \right) = {10.3^6}\\
\Leftrightarrow {10.3^{x + 1}} = {10.3^6}\\
\Leftrightarrow x + 1 = 6\\
\Leftrightarrow x = 5\\
Vậy\,x = 5\\
c){3.5^{x - 2}} + {4.5^{x - 3}} = {19.5^{10}}\\
\Leftrightarrow {5^{x - 3}}.\left( {3.5 + 4} \right) = {19.5^{10}}\\
\Leftrightarrow {5^{x - 3}}.19 = {19.5^{10}}\\
\Leftrightarrow x - 3 = 10\\
\Leftrightarrow x = 13\\
Vậy\,x = 13
\end{array}$
