In the Applications/Utilities folder, there is a program called Grapher.app which you can use to correctly write equations for LaTeX.
Make a 2D or 3D window and write the equation into Grapher. You can also use Grapher's different symbols. When you are finished, highlight the equation and command-click (right-click) and simply select "Copy LaTeX Expression." Now paste it into LaTeX
For example, it turned this equation:
y^(1/2)=cosx^2+cosz^3
Into this equation:
y^{\left( \frac{1}{2} \right)}=\cos x^{2}+\cos z^{3}
[robg adds: I haven't tested this one, but there are quite a few hints here on using LaTex with OS X. Also, in trying to understand LaTex better, I found this page, which has a ton of links to LaTex resources, as well as a nice one-page overview of LaTex.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050502201922646