How to draw large curly brackets?

[alexmahone]

How can I write "g(x) = x if x >= 0 and g(x) = -x for x < 0" on 2 lines using large curly brackets?

 

[earboth]

How can I write "g(x) = x if x >= 0 and g(x) = -x for x < 0" on 2 lines using large curly brackets?

If I understand your question correctly you mean (maybe) this(?):

$ g(x) = \left\{ \begin{array}{rcl} x\ &if& \ x\geq 0 \\ -x\ &if& \ x<0\end{array} \right. $

 

[alexmahone]

That's exactly what I meant. Thanks!

 

[Evgeny.Makarov]

There is also a more specialized cases environment:
$\begin{cases}
x&\text{if }x\ge0\\
-x&\text{if }x<0
\end{cases}$