Đáp án:
$\begin{array}{l}
a)Dkxd:\left\{ \begin{array}{l}
2 - x \ge 0\\
7 + x \ge 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \le 2\\
x \ge - 7
\end{array} \right.\\
\Rightarrow - 7 \le x \le 2\\
\Rightarrow TXD:D = \left[ { - 7;2} \right]\\
b)Dkxd:\left\{ \begin{array}{l}
5 - 2x \ge 0\\
x - 2 \ne 0\\
x - 1 > 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \le \dfrac{5}{2}\\
x \ne 2\\
x > 1
\end{array} \right.\\
\Rightarrow TXD:D = \left( {1;\dfrac{5}{2}} \right]\backslash \left\{ 2 \right\}\\
c)Dkxd:\left\{ \begin{array}{l}
3x - 2 \ge 0\\
4 - 3x > 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \ge \dfrac{2}{3}\\
x < \dfrac{4}{3}
\end{array} \right.\\
\Rightarrow \dfrac{2}{3} \le x < \dfrac{4}{3}\\
\Rightarrow TXD:D = \left[ {\dfrac{2}{3};\dfrac{4}{3}} \right)\\
d)DKxd:\left\{ \begin{array}{l}
x - 1 \ge 0\\
4 - x \ge 0\\
x \ne 2\\
x \ne 3
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \ge 1\\
x \le 4\\
x \ne 2\\
x \ne 3
\end{array} \right.\\
\Rightarrow 1 \le x \le 4;x \ne 2;x \ne 3\\
\Rightarrow TXD:D = \left[ {1;4} \right]\backslash \left\{ {2;3} \right\}\\
b)Dkxd:\left\{ \begin{array}{l}
x + 1 \ge 0\\
{x^2} - x - 6 \ne 0
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
x \ge - 1\\
\left( {x - 3} \right)\left( {x + 2} \right) \ne 0
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
x \ge - 1\\
x \ne 3\\
x \ne - 2
\end{array} \right.\\
\Rightarrow x \ge - 1;x \ne 3\\
\Rightarrow TXD:D = \left[ { - 1; + \infty } \right)\backslash \left\{ 3 \right\}\\
e)Dkxd:\left\{ \begin{array}{l}
2 - x \ge 0\\
x + 2 \ge 0\\
x \ne 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \le 2\\
x \ge - 2\\
x \ne 0
\end{array} \right.\\
\Rightarrow - 2 \le x \le 2;x \ne 0\\
\Rightarrow TXD:D = \left[ { - 2;2} \right]\backslash \left\{ 0 \right\}\\
g)Dkxd:\left\{ \begin{array}{l}
6 - x \ge 0\\
x - 1 \ge 0
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
x \le 6\\
x \ge 1
\end{array} \right.\\
\Rightarrow 1 \le x \le 6\\
\Rightarrow TXD:D = \left[ {1;6} \right]
\end{array}$
