The following site has a nice sandbox for testing out LaTeX code (and is a good reference as well).
http://www.forkosh.com/mimetextutorial.html
I used this all the time and the sandbox doesn't seem to be there any more. Am I the only one with this problem?
In the meantime, will use this space for some testing Tex code
[tex]C=kt \frac{L-x}{L}-\frac{kL^2}{D}\left(\frac{x}{3L}-\frac{x^2}{2L^2}+\frac{x^3}{6L^3}\right)+\frac{2kL^2}{D\pi^3}\sum_{n=1}^{\infty}\frac{1}{n^3}\sin{\left( \frac{n \pi x}{L} \right)}\exp{\left( -\frac{Dn^2 \pi^2 t}{L^2}\right)}[/tex]
[tex]C=kt \frac{L-x}{L}+k\frac{(L-x)^3}{8LD}+\frac{2kL^2}{D\pi^3}\sum_{n=1}^{\infty}\frac{1}{n^3}\sin{\left( \frac{n \pi x}{L} \right)}\exp{\left( -\frac{Dn^2 \pi^2 t}{L^2}\right)}[/tex]