Đáp án:
$1)x∉(2;5)$
$2)x∉(-5;0);(0;+∞)$
$3)\left[ \begin{array}{l}x∈[0;+∞)\\x∈(-∞;5]\\x∈[-1;2]\end{array} \right.$
$4)x∈[6;+∞)$
Giải thích các bước giải:
$1)\begin{cases}\left[ \begin{array}{l}x≤3\\x≥5\end{array} \right.\\\left[ \begin{array}{l}x≤2\\x≥4\end{array} \right.\end{cases}⇔\left[ \begin{array}{l}x≤2\\5≤x≤2\\4≤x≤3\\x≥5\end{array} \right.⇔\left[ \begin{array}{l}x≤2\\x≥5\end{array} \right.⇔x∉(2;5)$
$2)\begin{cases}\begin{cases}x≤2\\x≤0\end{cases}\\\left[ \begin{array}{l}x≥0\\x≤-5\end{array} \right.\end{cases}⇔\begin{cases}x≤0\\\left[ \begin{array}{l}x≥0\\x≤-5\end{array} \right.\end{cases}⇔\left[ \begin{array}{l}x=0\\x≤-5\end{array} \right.$
$3)\left[ \begin{array}{l}x≥0\\x≤5\\\begin{cases}x≤2\\x≥-1\end{cases}\end{array} \right.⇔\left[ \begin{array}{l}x≥0\\x≤5\\-1≤x≤2\end{array} \right.$
$4)\begin{cases}\left[ \begin{array}{l}x≥0\\x≤0\end{array} \right.\\\begin{cases}x≥2\\x≥6\end{cases}\end{cases}⇔\begin{cases}\left[ \begin{array}{l}x≥0\\x≤0\end{array} \right.\\x≥6\end{cases}⇔\left[ \begin{array}{l}x≥6\\6≤x≤0\end{array} \right.⇔x≥6$
