=-2ab+2|ab|≥0

|a-b|？ ≥(|b|-|a|)？

|a-b|≥|(|b|-|a|)|≥|b|-|a|

|a-b|≥|b|-|a|

If a and b are real numbers, then: |a-b|≥|b|-|a|

In this case, the necessary and sufficient condition is that the equal sign of |a-b|≥|b|-|a| does not hold.

It is easier to discuss when it is established.

1.a，b & gt0a & lt； b

2.a、b & lt0a & gt； b

3.a=b

In these three cases, it is obvious that the equal sign holds.

And it includes all cases of b/a≥ 1, and its complement is the answer, that is, b/a.

Supplementary note: a=b=0 is not in the necessary and sufficient condition and does not affect the answer.