( 1)X+ 1≥0，X ≥- 1；

(2)X- 1≥0 and x ≥1;

(3)X？ -1≥0, that is, (X+ 1)(X- 1)≥0, so X≥ 1 or X≤- 1.

Since x must satisfy the above three equations at the same time, therefore:

The condition of this formula is: X≥ 1.