Giải thích các bước giải:
Các biểu thức đã cho có nghĩa khi:
\(\begin{array}{l}
11,\\
- \dfrac{2}{3} - 3x \ge 0 \Leftrightarrow \dfrac{2}{3} + 3x \le 0\\
\Leftrightarrow 3x \le - \dfrac{2}{3}\\
\Leftrightarrow x \le - \dfrac{2}{9}\\
14,\\
\left\{ \begin{array}{l}
\dfrac{5}{{2x + 3}} \ge 0\\
2x + 3 \ne 0
\end{array} \right. \Leftrightarrow 2x + 3 > 0 \Leftrightarrow x > - \dfrac{3}{2}\\
17,\\
\left\{ \begin{array}{l}
- x + 1 \ge 0\\
2 - x \ge 0
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x - 1 \le 0\\
x - 2 \le 0
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \le 1\\
x \le 2
\end{array} \right. \Leftrightarrow x \le 1\\
20,\\
\left\{ \begin{array}{l}
- x - 3 \ge 0\\
4 - x \ne 0
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x + 3 \le 0\\
x \ne 4
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \le - 3\\
x \ne 4
\end{array} \right. \Leftrightarrow x \le - 3\\
23,\\
\left\{ \begin{array}{l}
2 - x \ge 0\\
x + 2 > 0
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \le 2\\
x > - 2
\end{array} \right. \Leftrightarrow - 2 < x \le 2\\
26,\\
{x^2} + 4x + 4 \ge 0 \Leftrightarrow {\left( {x + 2} \right)^2} \ge 0,\,\,\,\forall x\\
29,\\
- {x^2} - 2x - 1 \ge 0 \Leftrightarrow {x^2} + 2x + 1 \le 0 \Leftrightarrow {\left( {x + 1} \right)^2} \le 0\\
\Rightarrow {\left( {x + 1} \right)^2} = 0 \Leftrightarrow x = - 1
\end{array}\)
