# How do I typeset this piecewise function?

What is the LaTeX code for this? There is a solution about how to code the function part, but I could not find out how to make all that equal to f(x). Please ignore the semicolons in the piecewise function.

You may be looking for the cases environment of the amsmath package.

\documentclass{article}
\usepackage{amsmath}  % for 'cases' env. and '\text' macro
\begin{document}
$f(x) = \begin{cases} 4x & x\le0 \text{ ise}\\ 3x^2 & x>0 \text{ ise} \end{cases}$
\end{document}

You can built also an array like the example shown below to reproduce the correct command \cases in these circumstances. The [.5em] it is the vertical spacing between the two equations that you can increase or decrease.

\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}

\begin{document}
$f(x)=\Bigl\{\begin{array}{ll} 4x & x\leq 0\, \text{ ise } \\ 3x^2 & x>0\, \text{ ise } \end{array}$

$f(x)=\Biggl\{\begin{array}{ll} 4x & x\leq 0\, \text{ ise } \\[.5em] 3x^2 & x>0\, \text{ ise } \end{array}$
\end{document}