Question

For `x>=a` and `x<=b` what can A and B to make X all numbers?

For `x>=a` and `x<=b` what can A and B to make X all numbers?

Answer 1

`a=b`

Explanation:

I assume that the case of the variables in your question can be ignored. (e.g. `a=A)`

Here we have two inequalities: `x>=a and x<=b`

I interpret your question to be asking us to find a condition relating `a and b` such that `x` can be the set of all real numbers: `x in (-oo,+oo)`

If you consider `a and b` to be two points on the real line then the only situation where both inequalities are satisfied with `x in (-oo,+oo)` is when `a and b` are coincident - have the same value on the real line.

Hence our condition relating `a and b` is `a=b`