Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}
C < 0\\
\Leftrightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x - 1 > 0\\
x + 2 < 0
\end{array} \right.\\
\left\{ \begin{array}{l}
x - 1 < 0\\
x + 2 > 0
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x > 1\\
x < - 2
\end{array} \right.\left( l \right)\\
\left\{ \begin{array}{l}
x < 1\\
x > - 2
\end{array} \right.
\end{array} \right.\\
\to - 2 < x < 1\\
C > 0\\
\Leftrightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x - 1 > 0\\
x + 2 > 0
\end{array} \right.\\
\left\{ \begin{array}{l}
x - 1 < 0\\
x + 2 < 0
\end{array} \right.
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
\left\{ \begin{array}{l}
x > 1\\
x > - 2
\end{array} \right.\\
\left\{ \begin{array}{l}
x < 1\\
x < - 2
\end{array} \right.
\end{array} \right.\\
\to \left[ \begin{array}{l}
x > 1\\
x < - 2
\end{array} \right.
\end{array}\)
