Đáp án:
$\begin{array}{l}
a)2{x^2} - 1 = 49\\
\Rightarrow 2{x^2} = 49 + 1 = 50\\
\Rightarrow {x^2} = 50:2 = 25\\
\Rightarrow x = 5/x = - 5\\
b)3\left| {x - 1} \right| - 27 = 0\\
\Rightarrow 3\left| {x - 1} \right| = 27\\
\Rightarrow \left| {x - 1} \right| = 9\\
\Rightarrow \left[ \begin{array}{l}
x - 1 = 9\\
x - 1 = - 9
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = 10\\
x = - 8
\end{array} \right.\\
c)\left( {3x + 9} \right).\left( {11 - x} \right) = 0\\
\Rightarrow \left[ \begin{array}{l}
3x + 9 = 0\\
11 - x = 0
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
3x = - 9\\
x = 11
\end{array} \right.\\
\Rightarrow \left[ \begin{array}{l}
x = - 3\\
x = 11
\end{array} \right.
\end{array}$
