Case equation without curly brace

I want to have a case equation without the left curly brace. I am using

\documentclass[11pt,a4paper]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsthm}

\begin{document}
$$\begin{cases} \frac{I}{Z}=12+\frac{7}{Z}[eV] & ,Z<13 \\ \frac{I}{Z}=9.76+58.8Z^{-1.19}[eV] & ,Z\geq13 \\ \end{cases}$$
\end{document}


which is perfect for my case, except for the big, left curly brace!

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I wasn't aware of that...So I will do so for the answers that really worked. Thank you! – Thanos Sep 17 '12 at 14:31

You may better use aligned:

\documentclass[11pt,a4paper]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsthm}

\begin{document}
\begin{aligned} \frac{I}{Z} &= 12+\frac{7}{Z}\;[eV], && Z<13 \\ \frac{I}{Z} &= 9.76+58.8Z^{-1.19}\;[eV], && Z\geq13 \end{aligned}
\end{document}


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I see the difference...You are right...The size is much better in that case! Thank you!!! – Thanos Sep 17 '12 at 14:29

Then use a regular array:

\documentclass{article}
\begin{document}
$$\renewcommand{\arraystretch}{1.3} \begin{array}{ll} \frac{I}{Z}=12+\frac{7}{Z}[eV], & Z<13 \\ \frac{I}{Z}=9.76+58.8Z^{-1.19}[eV], & Z\geq13 \end{array}$$
\end{document}


The alignment specification of {ll} inserts the contents left-aligned in both columns, while a redefinition of \arraystretch adds some vertical padding to each row. See Column padding in tables.

Since each element inside an array is set in \textstyle, fractions are smaller than usual by default. Adding \displaystyle will increase the fraction presentation, similar to amsmath's \dfrac.

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@Werner -- i really think the \ at the end of the last line of the array is a bad idea. i know it was in the original question, so i should probably comment it there, but this comment will get to you more reliably, as well as to the op. – barbara beeton Sep 21 '12 at 20:58