Đáp án:
$\begin{array}{l}
a)\sqrt {4\left( {x - 1} \right)} - \sqrt {x - 1} + \sqrt {9x - 9} = 8\\
Dkxd:x \ge 1\\
\Rightarrow 2\sqrt {x - 1} - \sqrt {x - 1} + 3\sqrt {x - 1} = 8\\
\Rightarrow 4\sqrt {x - 1} = 8\\
\Rightarrow \sqrt {x - 1} = 2\\
\Rightarrow x - 1 = 4\\
\Rightarrow x = 5\left( {tmdk} \right)\\
b)\left\{ \begin{array}{l}
2x + y = 7\\
x - 3y = - 7
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
2x + y = 7\\
2x - 6y = - 14
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
7y = 21\\
x - 3y = - 7
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
y = 3\\
x = 3y - 7 = 2
\end{array} \right.\\
\Rightarrow \left( {x;y} \right) = \left( {2;3} \right)\\
2)a)\left( \Delta \right)//\left( d \right)\\
\Rightarrow \left( \Delta \right):x + y + c = 0\left( {c \ne - 10} \right)\\
A\left( {0;1} \right) \in \left( \Delta \right)\\
\Rightarrow 0 + 1 + c = 0\\
\Rightarrow c = - 1\left( {tmdk} \right)\\
\Rightarrow \left( \Delta \right):x + y - 1 = 0\\
hay\,x + y = 1\\
b)a.c < 0\\
\Rightarrow {m^2} - 7m + 12 < 0\\
\Rightarrow {m^2} - 3m - 4m + 12 < 0\\
\Rightarrow \left( {m - 3} \right)\left( {m - 4} \right) < 0\\
\Rightarrow 3 < m < 4
\end{array}$
