\(\begin{array}{l}
f)\,DK:\left\{ \begin{array}{l}
x > a\\
x \le 2a + 6
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
a \le 2a + 6\\
a \le x \le 2a + 6
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
a \ge - 3\\
a \le x \le 2a + 6
\end{array} \right.\\
D = \left[ {a;2a + 6} \right]\\
ycbt \Rightarrow \left( { - 1;0} \right) \subset \left[ {a;2a + 6} \right] \Rightarrow a \le - 1 < 0 \le 2a + 6 \Leftrightarrow - 3 \le a \le - 1
\end{array}\)
