a)
a = -3 => |a| = |-3| = 3a = 0 => |a| = |0| = 0a = 7 => |a| = |7| = 7a = -2 => |a| = |-2| = 2a = 1 => |a| = |1| = 1a = -9 => |a| = |-9| = 9a = 4 => |a| = |4| = 4b)
\(\left|a\right|=5\Rightarrow\begin{cases}a=5\\a=-5\end{cases}\)\(\left|a\right|=10\Rightarrow\begin{cases}a=10\\a=-10\end{cases}\)\(\left|a\right|=0\Rightarrow a=0\)\(\left|a\right|=-6\Rightarrow a\in\varnothing\)(|a| ko thể là số âm)\(\left|a\right|=1\Rightarrow\begin{cases}a=1\\a=-1\end{cases}\)