- The absolute value of a real number x or the \left| x \right|, is the distance x lies from 0 on a number line.
- The absolute value of a real number is never negative or the \left| x \right|\ge 0
- \left| x \right| =\sqrt { { x }^{ 2 } }
- Piecewise: \left| x \right| =\begin{cases} x,\quad \quad if\quad x\ge 0 \\ -x,\quad if\quad x<0 \end{cases}