"Illegal character in array arg"?

2,729

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}
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Another User
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Another User

Updated on December 12, 2020

Comments

  • Another User
    Another User almost 3 years

    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?

    • Troy
      Troy almost 6 years
      Welcome to TeX.SE! It's ll, not 11. l, as in left-align.