Ответ: 1) [0; 9]
\[9x - x^2 \ge 0 \Rightarrow x(9 - x) \ge 0\]
\[x(9 - x) = 0 \Rightarrow x = 0, x = 9\]
----(-)--[0]----(+)----[9]----(-)--->
\[x \in [0; 9]\]