Examples:

$\frac{1}{x+1}$
$e^{i \pi} + 1 = 0$
$\mathbf{E}\cdot\mathrm{d}\mathbf{S} = \frac{1}{\varepsilon_0} \iiint_\Omega \rho \,\mathrm{d}V$


N.B. If you wish to use the dollar sign in your question, here is how you can obtain it, without messing up your LaTeX format.

 $$ 500 or \$ 500

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