Question

Give an example of the set which can be written in the set builder form but cannot be written in the roster form.

Answer 1

The set of rational numbers Q can be written in the set builder form as Q = $\left\{\frac{a}{b}|a\in \mathrm{I},b\in \mathrm{I}\mathrm{and}b\ne 0\right\}$. However, it cannot be written in the roster form.