emacs/LaTeX error for first time LaTeX user

Question

I am using LaTeX with Emacs for the first time. I am getting the following error message:

! Missing $ inserted

This is the code I put in:

center\[
$$Q(t) = Pi a^2 \sqrt{2gh}$$

]

What am I doing wrong?

Answer 1

As far as I understand, you would like to achieve something like the following:

\[
Q(t) = \Pi a^2 \sqrt{2gh}
\]

I replaced the $$ in your code with \[ and \] respectively. Please see e.g. this thread for some detailed explanations on why the use of \[ and \] is preferable to $$ in LaTeX.

Answer 2

It's only a single '$' at each side. Although if you're trying to center the equation anyway, your best bet would be to use

\begin{equation*}
Q(t) = \Pi a^2 \sqrt{2gh}
\end{equation*}

This will center it on its own line, and the * simply says not to number the equation.