Vbraces.tex

$$
sign(x) = \left\{
    \begin{array}\\
        1 & \mbox{if } \ x \in \mathbf{N}^* \\
        0 & \mbox{if } \ x = 0 \\
        -1 & \mbox{else.}
    \end{array}
\right.
$$

\\

$$
 \left.
    \begin{array} \\
        \alpha^2 = \sqrt5 \\
        \alpha \geq 0 
    \end{array}
\right \}=\alpha = 5 
$$