Test

\begin{array}{ccccc} CH_3& -& CH & -& CH_2-& CH-& COOH \\ && |& && |& \\ & & CH3&& &NH_2 &&\end{array}
\begin{array}{ccccc} CH_3& -& CH & -& CH_3 \\ & & | & & \\ & & OH &&\end{array}
$\left\{
    \begin{array}{rl}
      \text{si}& p>0 & \text{pour tout} & x,y >0\\
   \text{si} &p<0 & \text{pour tout} & x,y<0
  \end{array}
    \right.$

$\left\{
    \begin{array}{rl}
      0\leq r <b \\
  0\leq r'<b
  \end{array}
    \right. \Rightarrow \left\{
    \begin{array}{rl}
      -b< -r \leq 0 \\
  0\leq r'<b
  \end{array}
    \right.$ // select all 'a' elements that have a title attribute $('a[title]') // select all 'a' elements whose href attribute begins with 'mailto' 
$('a[href^="mailto:"]')

$\[
\begin{array}{l}
   sin cos \\
   sin \! cos \\
   sin \, cos \\
   sin \  cos \\
   sin \quad cos \\
   sin \qquad cos \\
\end{array}
\]$

\begin{eqnarray}
   x_1 & = & valeur_1 \\
   x_2 & = & valeur_2 \\
   x_3 & = & valeur_3
  \end{eqnarray}

\begin{array}{lcl} z & = & a \\ f(x,y,z) & = & x + y + z \end{array}

\begin{array}{lcl} z & = & a \\ f(x,y,z) & = & x + y + z \end{array}

\begin{array}{rcr} z & = & a \\ f(x,y,z) & = & x + y + z \end{array}

\begin{array}{rcr} z & = & a \\ f(x,y,z) & = & x + y + z \end{array}

\begin{array}{rcl} f: R^3 & \to & R \\ (x,y,z) & \to & x + y + z \\ f(x,y,z) & = & x + y + z \end{array}

\begin{array}{rcl} f: R^3 & \to & R \\ (x,y,z) & \to & x + y + z \\ f(x,y,z) & = & x + y + z \end{array}

\begin{array} {lcl} f(x) & = & (a+b)^2 \\ & = & a^2+2ab+b^2 \end{array}

\begin{array} {lcl} f(x) & = & (a+b)^2 \\ & = & a^2+2ab+b^2 \end{array}

$$
\begin{matrix}
a & b \\
c & d
\end{matrix}
\quad
\begin{pmatrix}
a & b \\
c & d
\end{pmatrix}
\quad
\begin{bmatrix}
a & b \\
c & d
\end{bmatrix}
\quad
\begin{vmatrix}
a & b \\
c & d
\end{vmatrix}
\quad
\begin{Vmatrix}
a & b \\
c & d
\end{Vmatrix}
$$

$\left\{
    \begin{array}{lcl}
      x-1 &=& -5k\\
y-2 &=& -k\\
z-3 &=& 2k
  \end{array}
  $