Đáp án:
$\begin{array}{l}
6)Dkxd:\left\{ \begin{array}{l}
4x - 8 \ge 0\\
x - 2 \ge 0
\end{array} \right. \Leftrightarrow x \ge 2\\
\sqrt {4x - 8} = 2\sqrt {x - 2} \\
\Leftrightarrow 4x - 8 = 4.\left( {x - 2} \right)\\
\Leftrightarrow 4x - 8 = 4x - 8\left( {tm} \right)\\
Vậy\,x \ge 2\\
7)Dkxd:\left\{ \begin{array}{l}
3x - 2 \ge 0\\
- 5x \ge 0
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \ge \dfrac{2}{3}\\
x \le 0
\end{array} \right.\left( {ktm} \right)
\end{array}$
Vậy phương trình vô nghiệm.
