# “Illegal character in array arg”?

Beginner here, I have been trying to use Overleaf after writing on ShareLaTex but the text isn't being correctly read. This is the original code:

\left\{
\begin{array}{11}
\frac{x^2+2x}{x+1} \geq 0 \\
x > -1 \\
\end{array}
\right.


And this is the error I get:

LaTeX Error: Illegal character in array arg.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
...

l.43 \begin{array}{11}


What did I do wrong?

• Welcome to TeX.SE! It's ll, not 11. l, as in left-align. – Troy Dec 11 '17 at 16:18

Your code works in the following way (see Troy's comment)

\documentclass{article}
\begin{document}
$\left\{ \begin{array}{l} % not \begin{array}{11} \frac{x^2+2x}{x+1} \geq 0 \\ x > -1 \\ \end{array} \right.$
\end{document}


but it is better:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\left\{ \begin{aligned} \frac{x^2+2x}{x+1} &\geq 0 \\ x &> -1 \\ \end{aligned} \right.
\end{document}