−1≤a≤0⇒{0≤a+1a−1<0⇒{|a+1|=a+1|a−1|=1−a

=> |a + 1| + |a - 1| = a + 1 + 1 - a = 2

\(-1\le a\le0\Rightarrow\left\{{}\begin{matrix}0\le a+1\\a-1< 0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}\left|a+1\right|=a+1\\\left|a-1\right|=1-a\end{matrix}\right.\)

=> |a + 1| + |a - 1| = a + 1 + 1 - a = 2