Number that, when written in decimal notation, is an unlimited decimal sequence periodic or not.

### Notations

- The symbol that represents the set of real numbers is the letter \(\mathbb{R}\).
- The symbol that represents the set of real positive numbers is: \(\mathbb{R}_{+}\) = {
*x*∈ \(\mathbb{R}\) |*x*≥ 0} - The symbol that represents the set of real negative numbers is:\(\mathbb{R}_{–}\) = {
*x*∈ \(\mathbb{R}\) |*x*≤ 0} - The symbol that represents the set of the non-zero real numbers is: \(\mathbb{R}{^*}\) = {
*x*∈ \(\mathbb{R}\) |*x*≠ 0} - The symbol that represents the set of strictly positive real numbers is: \(\mathbb{R}_{+}^{*}\) = {
*x*∈ \(\mathbb{R}\) |*x*> 0} - The symbol that represents the set of strictly negative real numbers is: \(\mathbb{R}_{–}^{*}\) = {
*x*∈ \(\mathbb{R}\) |*x*< 0}