Đáp án:
$\begin{array}{l}
a){\left( {\dfrac{3}{4}} \right)^x} = \dfrac{{{2^8}}}{{{3^4}}}\\
\Leftrightarrow {\left( {\dfrac{3}{4}} \right)^x} = \dfrac{{{2^{2.4}}}}{{{3^4}}}\\
\Leftrightarrow {\left( {\dfrac{3}{4}} \right)^x} = \dfrac{{{4^4}}}{{{3^4}}}\\
\Leftrightarrow {\left( {\dfrac{3}{4}} \right)^x} = {\left( {\dfrac{4}{3}} \right)^4}\\
\Leftrightarrow {\left( {\dfrac{3}{4}} \right)^x} = {\left( {\dfrac{3}{4}} \right)^{ - 4}}\\
\Leftrightarrow x = - 4\\
Vậy\,x = - 4\\
b){\left( {x + 2} \right)^2} = 36\\
\Leftrightarrow \left[ \begin{array}{l}
x + 2 = 6\\
x + 2 = - 6
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 4\\
x = - 8
\end{array} \right.\\
Vậy\,x = 4;x = - 8\\
c){5^{\left( {x - 2} \right)\left( {x + 3} \right)}} = 1\\
\Leftrightarrow \left( {x - 2} \right)\left( {x + 3} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x - 2 = 0\\
x + 3 = 0
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 2\\
x = - 3
\end{array} \right.\\
Vậy\,x = 2;x = - 3
\end{array}$
