$\begin{cases}
\ \left| x \right| = x \hspace{0.9em} se \hspace{0.9em} x \geq 0
\\[1 em]
\ \left| x \right| = -x \hspace{0.9em} se \hspace{0.9em} x < 0
\end{cases}$
2. Propriedades do módulo
$\left| x.y \right|= \left|x\right|.\left|y \right|$
$ \left| \dfrac{ x }{y} \right| =\dfrac{\left|x\right|}{\left|y\right|} \quad$ $\left( y \neq 0 \right)$
$ \left|x+y\right|\le \left| x \right| + \left| y \right|$
$ \sqrt[2]{x^{2}}=\left| x \right| $
$ \left| x \right| =\left| -x \right| $
$ x^{2}=\left| x \right|^{2}=\left| x^{2} \right|$