It should be understood this way.
F (x) ≤| x-4 |, that is | x+a |≤| x-4 |-| x-2 |
As shown in the figure, because | x+a | >;; =0
In order to make | x+a |≤| x-4 |-x-2 | meaningful, you must have | x-4 |-x-2 | = 0 and get x.
When 2
When x
Then calculate the result.
Actually this is the best algorithm! Do you agree?