Đáp án:
b. \(\left\{ \begin{array}{l}
x \le 3\\
x \ne - \dfrac{{112}}{3}
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
a.DK:\left\{ \begin{array}{l}
\dfrac{{7x - 8}}{{4 - 4x}} \ge 0\\
4 - 4x \ne 0
\end{array} \right.\\
\to \left\{ \begin{array}{l}
\left[ \begin{array}{l}
\left\{ \begin{array}{l}
7x - 8 \ge 0\\
4 - 4x > 0
\end{array} \right.\\
\left\{ \begin{array}{l}
7x - 8 \le 0\\
4 - 4x < 0
\end{array} \right.
\end{array} \right.\\
x \ne 1
\end{array} \right. \to \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x \ge \dfrac{8}{7}\\
x < 1
\end{array} \right.\left( l \right)\\
\left\{ \begin{array}{l}
x \le \dfrac{8}{7}\\
x > 1
\end{array} \right.
\end{array} \right.\\
\to 1 < x \le \dfrac{8}{7}\\
b.DK:\left\{ \begin{array}{l}
9 - 3x \ge 0\\
\sqrt {9 - 3x} \ne 11
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x \le 3\\
9 - 3x \ne 121
\end{array} \right.\\
\to \left\{ \begin{array}{l}
x \le 3\\
x \ne - \dfrac{{112}}{3}
\end{array} \right.
\end{array}\)
