Can anyone please help me with this example from Spivak? I am math autodidact.
I have to express this without absolute value: $$a-|a-|a||$$ The answer is $$\begin{cases}a&a\ge0\\ 3a&a<0\end{cases}$$ All examples went OK, but I dont know this one. I might understand answer by intuition but I can't do it rigorously. Thanks.