Question

Which of the following has no solutlon? (×|×0) (×|×0) (×|×0)

Answer 1

The set:

$x|x<0\text{ and x|}x>0$

has no solutions. This follows from the fact that the set ask for a number that is at the same time less than zero a more than zero. And there are no real number that fullfils both conditions.