Symbols:R

The Set of Real Numbers

 * $\R$

The set of real numbers.

Its $\LaTeX$ code is \mathbb R or (preferably) \R.

MediaWiki $\LaTeX$ also allows \reals, but MathJax does not recognise that as a valid code.

Some authors use $R$.

The Set of Non-Zero Real Numbers

 * $\R^*$

The set of non-zero real numbers:
 * $\R^* = \R - \left\{{0}\right\}$

Its $\LaTeX$ code is \mathbb R^* or (preferably) \R^*.

MediaWiki $\LaTeX$ also allows \reals^*, but MathJax does not recognise that as a valid code.

The Set of Non-Negative Real Numbers

 * $\R_+$

The set of non-negative real numbers:
 * $\R_+ = \left\{{x \in \R: x \ge 0}\right\}$

Its $\LaTeX$ code is \mathbb R_+ or (preferably) \R_+.

MediaWiki $\LaTeX$ also allows \reals_+</tt>, but MathJax does not recognise that as a valid code.

The Set of Strictly Positive Real Numbers

 * $\R_+^*$

The set of strictly positive real numbers:
 * $\R_+^* = \left\{{x \in \R: x > 0}\right\}$

Its $\LaTeX$ code is \mathbb R_+^*</tt> or (preferably) \R_+^*</tt>.

MediaWiki $\LaTeX$ also allows \reals_+^*</tt>, but MathJax does not recognise that as a valid code.