Đáp án:
\(\begin{array}{l}
j)3 > x \ge \dfrac{1}{2}\\
k)\left\{ \begin{array}{l}
x \ge 3\\
x \ne 4
\end{array} \right.
\end{array}\)
\(l)\left\{ \begin{array}{l}
4 \ge x\\
x \ge - 2
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
j)DK:\left\{ \begin{array}{l}
2x - 1 \ge 0\\
3 - x > 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
3 > x\\
x \ge \dfrac{1}{2}
\end{array} \right.\\
\to 3 > x \ge \dfrac{1}{2}\\
k)DK:\left\{ \begin{array}{l}
x \ge 0\\
x - 3 \ge 0\\
\sqrt {x - 3} - 1 \ne 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x \ge 3\\
x - 3 \ne 1
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x \ge 3\\
x \ne 4
\end{array} \right.
\end{array}\)
\(\begin{array}{l}
l)DK:\left\{ \begin{array}{l}
4 - x \ge 0\\
x + 2 \ge 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
4 \ge x\\
x \ge - 2
\end{array} \right.
\end{array}\)
