Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}
C2:\left\{ \begin{array}{l}
a > 0\\
{x_1}.{x_2} = \frac{c}{a} > 0\\
{x_1} + {x_2} = \frac{{ - b}}{a} > 0
\end{array} \right. \to \left\{ \begin{array}{l}
a > 0\\
c > 0\\
b < 0
\end{array} \right.\\
C3:\\
\left\{ \begin{array}{l}
\left( {3 - x} \right)\left( {x - 1} \right) \le 0\\
- x > - 4
\end{array} \right. \to \left\{ \begin{array}{l}
\left[ \begin{array}{l}
x > 3\\
x < 1
\end{array} \right.\\
x < 4
\end{array} \right.\\
\to \left[ \begin{array}{l}
3 < x < 4\\
x < 1
\end{array} \right.
\end{array}\)
